diff mbox series

pgo: add clang's Profile Guided Optimization infrastructure

Message ID 20210111081821.3041587-1-morbo@google.com (mailing list archive)
State New
Headers show
Series pgo: add clang's Profile Guided Optimization infrastructure | expand

Commit Message

Bill Wendling Jan. 11, 2021, 8:18 a.m. UTC
From: Sami Tolvanen <samitolvanen@google.com>

Enable the use of clang's Profile-Guided Optimization[1]. To generate a
profile, the kernel is instrumented with PGO counters, a representative
workload is run, and the raw profile data is collected from
/sys/kernel/debug/pgo/profraw.

The raw profile data must be processed by clang's "llvm-profdata" tool before
it can be used during recompilation:

  $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
  $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw

Multiple raw profiles may be merged during this step.

The data can be used either by the compiler if LTO isn't enabled:

    ... -fprofile-use=vmlinux.profdata ...

or by LLD if LTO is enabled:

    ... -lto-cs-profile-file=vmlinux.profdata ...

This initial submission is restricted to x86, as that's the platform we know
works. This restriction can be lifted once other platforms have been verified
to work with PGO.

Note that this method of profiling the kernel is clang-native and isn't
compatible with clang's gcov support in kernel/gcov.

[1] https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Co-developed-by: Bill Wendling <morbo@google.com>
Signed-off-by: Bill Wendling <morbo@google.com>
---
 Documentation/dev-tools/index.rst     |   1 +
 Documentation/dev-tools/pgo.rst       | 127 +++++++++
 MAINTAINERS                           |   9 +
 Makefile                              |   3 +
 arch/Kconfig                          |   1 +
 arch/arm/boot/bootp/Makefile          |   1 +
 arch/arm/boot/compressed/Makefile     |   1 +
 arch/arm/vdso/Makefile                |   3 +-
 arch/arm64/kernel/vdso/Makefile       |   3 +-
 arch/arm64/kvm/hyp/nvhe/Makefile      |   1 +
 arch/mips/boot/compressed/Makefile    |   1 +
 arch/mips/vdso/Makefile               |   1 +
 arch/nds32/kernel/vdso/Makefile       |   4 +-
 arch/parisc/boot/compressed/Makefile  |   1 +
 arch/powerpc/kernel/Makefile          |   6 +-
 arch/powerpc/kernel/trace/Makefile    |   3 +-
 arch/powerpc/kernel/vdso32/Makefile   |   1 +
 arch/powerpc/kernel/vdso64/Makefile   |   1 +
 arch/powerpc/kexec/Makefile           |   3 +-
 arch/powerpc/xmon/Makefile            |   1 +
 arch/riscv/kernel/vdso/Makefile       |   3 +-
 arch/s390/boot/Makefile               |   1 +
 arch/s390/boot/compressed/Makefile    |   1 +
 arch/s390/kernel/Makefile             |   1 +
 arch/s390/kernel/vdso64/Makefile      |   3 +-
 arch/s390/purgatory/Makefile          |   1 +
 arch/sh/boot/compressed/Makefile      |   1 +
 arch/sh/mm/Makefile                   |   1 +
 arch/sparc/vdso/Makefile              |   1 +
 arch/x86/Kconfig                      |   1 +
 arch/x86/boot/Makefile                |   1 +
 arch/x86/boot/compressed/Makefile     |   1 +
 arch/x86/entry/vdso/Makefile          |   1 +
 arch/x86/kernel/vmlinux.lds.S         |   2 +
 arch/x86/platform/efi/Makefile        |   1 +
 arch/x86/purgatory/Makefile           |   1 +
 arch/x86/realmode/rm/Makefile         |   1 +
 arch/x86/um/vdso/Makefile             |   1 +
 drivers/firmware/efi/libstub/Makefile |   1 +
 drivers/s390/char/Makefile            |   1 +
 include/asm-generic/vmlinux.lds.h     |  44 +++
 kernel/Makefile                       |   1 +
 kernel/pgo/Kconfig                    |  34 +++
 kernel/pgo/Makefile                   |   5 +
 kernel/pgo/fs.c                       | 382 ++++++++++++++++++++++++++
 kernel/pgo/instrument.c               | 147 ++++++++++
 kernel/pgo/pgo.h                      | 206 ++++++++++++++
 scripts/Makefile.lib                  |  10 +
 48 files changed, 1017 insertions(+), 9 deletions(-)
 create mode 100644 Documentation/dev-tools/pgo.rst
 create mode 100644 kernel/pgo/Kconfig
 create mode 100644 kernel/pgo/Makefile
 create mode 100644 kernel/pgo/fs.c
 create mode 100644 kernel/pgo/instrument.c
 create mode 100644 kernel/pgo/pgo.h

Comments

Sedat Dilek Jan. 11, 2021, 8:39 a.m. UTC | #1
On Mon, Jan 11, 2021 at 9:18 AM 'Bill Wendling' via Clang Built Linux
<clang-built-linux@googlegroups.com> wrote:
>
> From: Sami Tolvanen <samitolvanen@google.com>
>
> Enable the use of clang's Profile-Guided Optimization[1]. To generate a
> profile, the kernel is instrumented with PGO counters, a representative
> workload is run, and the raw profile data is collected from
> /sys/kernel/debug/pgo/profraw.
>
> The raw profile data must be processed by clang's "llvm-profdata" tool before
> it can be used during recompilation:
>
>   $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
>   $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
>
> Multiple raw profiles may be merged during this step.
>
> The data can be used either by the compiler if LTO isn't enabled:
>
>     ... -fprofile-use=vmlinux.profdata ...
>
> or by LLD if LTO is enabled:
>
>     ... -lto-cs-profile-file=vmlinux.profdata ...
>
> This initial submission is restricted to x86, as that's the platform we know
> works. This restriction can be lifted once other platforms have been verified
> to work with PGO.
>
> Note that this method of profiling the kernel is clang-native and isn't
> compatible with clang's gcov support in kernel/gcov.
>
> [1] https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
>

Hi Bill and Sami,

I have seen the pull-request in the CBL issue tracker and had some
questions in mind.

Good you send this.

First of all, I like to fetch any development stuff easily from a Git
repository.
Can you offer this, please?
What is the base for your work?
I hope this is (fresh released) Linux v5.11-rc3.

I myself had some experiences with a PGO + ThinLTO optimized LLVM
toolchain built with the help of tc-build.
Here it takes very long to build it.

This means I have some profile-data archived.
Can I use it?

Is an own PGO + ThinLTO optimized LLVM toolchain pre-requirement for
this or not?
That is one of my important questions.

Thanks for your work.

Regards,
- Sedat -

> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> Co-developed-by: Bill Wendling <morbo@google.com>
> Signed-off-by: Bill Wendling <morbo@google.com>
> ---
>  Documentation/dev-tools/index.rst     |   1 +
>  Documentation/dev-tools/pgo.rst       | 127 +++++++++
>  MAINTAINERS                           |   9 +
>  Makefile                              |   3 +
>  arch/Kconfig                          |   1 +
>  arch/arm/boot/bootp/Makefile          |   1 +
>  arch/arm/boot/compressed/Makefile     |   1 +
>  arch/arm/vdso/Makefile                |   3 +-
>  arch/arm64/kernel/vdso/Makefile       |   3 +-
>  arch/arm64/kvm/hyp/nvhe/Makefile      |   1 +
>  arch/mips/boot/compressed/Makefile    |   1 +
>  arch/mips/vdso/Makefile               |   1 +
>  arch/nds32/kernel/vdso/Makefile       |   4 +-
>  arch/parisc/boot/compressed/Makefile  |   1 +
>  arch/powerpc/kernel/Makefile          |   6 +-
>  arch/powerpc/kernel/trace/Makefile    |   3 +-
>  arch/powerpc/kernel/vdso32/Makefile   |   1 +
>  arch/powerpc/kernel/vdso64/Makefile   |   1 +
>  arch/powerpc/kexec/Makefile           |   3 +-
>  arch/powerpc/xmon/Makefile            |   1 +
>  arch/riscv/kernel/vdso/Makefile       |   3 +-
>  arch/s390/boot/Makefile               |   1 +
>  arch/s390/boot/compressed/Makefile    |   1 +
>  arch/s390/kernel/Makefile             |   1 +
>  arch/s390/kernel/vdso64/Makefile      |   3 +-
>  arch/s390/purgatory/Makefile          |   1 +
>  arch/sh/boot/compressed/Makefile      |   1 +
>  arch/sh/mm/Makefile                   |   1 +
>  arch/sparc/vdso/Makefile              |   1 +
>  arch/x86/Kconfig                      |   1 +
>  arch/x86/boot/Makefile                |   1 +
>  arch/x86/boot/compressed/Makefile     |   1 +
>  arch/x86/entry/vdso/Makefile          |   1 +
>  arch/x86/kernel/vmlinux.lds.S         |   2 +
>  arch/x86/platform/efi/Makefile        |   1 +
>  arch/x86/purgatory/Makefile           |   1 +
>  arch/x86/realmode/rm/Makefile         |   1 +
>  arch/x86/um/vdso/Makefile             |   1 +
>  drivers/firmware/efi/libstub/Makefile |   1 +
>  drivers/s390/char/Makefile            |   1 +
>  include/asm-generic/vmlinux.lds.h     |  44 +++
>  kernel/Makefile                       |   1 +
>  kernel/pgo/Kconfig                    |  34 +++
>  kernel/pgo/Makefile                   |   5 +
>  kernel/pgo/fs.c                       | 382 ++++++++++++++++++++++++++
>  kernel/pgo/instrument.c               | 147 ++++++++++
>  kernel/pgo/pgo.h                      | 206 ++++++++++++++
>  scripts/Makefile.lib                  |  10 +
>  48 files changed, 1017 insertions(+), 9 deletions(-)
>  create mode 100644 Documentation/dev-tools/pgo.rst
>  create mode 100644 kernel/pgo/Kconfig
>  create mode 100644 kernel/pgo/Makefile
>  create mode 100644 kernel/pgo/fs.c
>  create mode 100644 kernel/pgo/instrument.c
>  create mode 100644 kernel/pgo/pgo.h
>
> diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst
> index f7809c7b1ba9e..8d6418e858062 100644
> --- a/Documentation/dev-tools/index.rst
> +++ b/Documentation/dev-tools/index.rst
> @@ -26,6 +26,7 @@ whole; patches welcome!
>     kgdb
>     kselftest
>     kunit/index
> +   pgo
>
>
>  .. only::  subproject and html
> diff --git a/Documentation/dev-tools/pgo.rst b/Documentation/dev-tools/pgo.rst
> new file mode 100644
> index 0000000000000..2ed7f549b20ef
> --- /dev/null
> +++ b/Documentation/dev-tools/pgo.rst
> @@ -0,0 +1,127 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +===============================
> +Using PGO with the Linux kernel
> +===============================
> +
> +Clang's profiling kernel support (PGO_) enables profiling of the Linux kernel
> +when building with Clang. The profiling data is exported via the ``pgo``
> +debugfs directory.
> +
> +.. _PGO: https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
> +
> +
> +Preparation
> +===========
> +
> +Configure the kernel with:
> +
> +.. code-block:: make
> +
> +   CONFIG_DEBUG_FS=y
> +   CONFIG_PGO_CLANG=y
> +
> +Note that kernels compiled with profiling flags will be significantly larger
> +and run slower.
> +
> +Profiling data will only become accessible once debugfs has been mounted:
> +
> +.. code-block:: sh
> +
> +   mount -t debugfs none /sys/kernel/debug
> +
> +
> +Customization
> +=============
> +
> +You can enable or disable profiling for individual file and directories by
> +adding a line similar to the following to the respective kernel Makefile:
> +
> +- For a single file (e.g. main.o)
> +
> +  .. code-block:: make
> +
> +     PGO_PROFILE_main.o := y
> +
> +- For all files in one directory
> +
> +  .. code-block:: make
> +
> +     PGO_PROFILE := y
> +
> +To exclude files from being profiled use
> +
> +  .. code-block:: make
> +
> +     PGO_PROFILE_main.o := n
> +
> +and
> +
> +  .. code-block:: make
> +
> +     PGO_PROFILE := n
> +
> +Only files which are linked to the main kernel image or are compiled as kernel
> +modules are supported by this mechanism.
> +
> +
> +Files
> +=====
> +
> +The PGO kernel support creates the following files in debugfs:
> +
> +``/sys/kernel/debug/pgo``
> +       Parent directory for all PGO-related files.
> +
> +``/sys/kernel/debug/pgo/reset``
> +       Global reset file: resets all coverage data to zero when written to.
> +
> +``/sys/kernel/debug/profraw``
> +       The raw PGO data that must be processed with ``llvm_profdata``.
> +
> +
> +Workflow
> +========
> +
> +The PGO kernel can be run on the host or test machines. The data though should
> +be analyzed with Clang's tools from the same Clang version as the kernel was
> +compiled. Clang's tolerant of version skew, but it's easier to use the same
> +Clang version.
> +
> +The profiling data is useful for optimizing the kernel, analyzing coverage,
> +etc. Clang offers tools to perform these tasks.
> +
> +Here is an example workflow for profiling an instrumented kernel with PGO and
> +using the result to optimize the kernel:
> +
> +1) Install the kernel on the TEST machine.
> +
> +2) Reset the data counters right before running the load tests
> +
> +   .. code-block:: sh
> +
> +      echo 1 > /sys/kernel/debug/pgo/reset
> +
> +3) Run the load tests.
> +
> +4) Collect the raw profile data
> +
> +   .. code-block:: sh
> +
> +      cp -a /sys/kernel/debug/pgo/profraw /tmp/vmlinux.profraw
> +
> +5) (Optional) Download the raw profile data to the HOST machine.
> +
> +6) Process the raw profile data
> +
> +   .. code-block:: sh
> +
> +      llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> +
> +   Note that multiple raw profile data files can be merged during this step.
> +
> +7) Rebuild the kernel using the profile data (PGO disabled)
> +
> +   .. code-block:: sh
> +
> +      make ... KCLAGS=-fprofile-use=vmlinux.profdata
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 6390491b07e51..7a98bdaab9861 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -13955,6 +13955,15 @@ S:     Maintained
>  F:     include/linux/personality.h
>  F:     include/uapi/linux/personality.h
>
> +PGO BASED KERNEL PROFILING
> +M:     Sami Tolvanen <samitolvanen@google.com>
> +M:     Bill Wendling <wcw@google.com>
> +R:     Nathan Chancellor <natechancellor@gmail.com>
> +R:     Nick Desaulniers <ndesaulniers@google.com>
> +S:     Supported
> +F:     Documentation/dev-tools/pgo.rst
> +F:     kernel/pgo
> +
>  PHOENIX RC FLIGHT CONTROLLER ADAPTER
>  M:     Marcus Folkesson <marcus.folkesson@gmail.com>
>  L:     linux-input@vger.kernel.org
> diff --git a/Makefile b/Makefile
> index 8b2c3f88ee5ea..4f42957c78134 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -659,6 +659,9 @@ endif # KBUILD_EXTMOD
>  # Defaults to vmlinux, but the arch makefile usually adds further targets
>  all: vmlinux
>
> +CFLAGS_PGO_CLANG := -fprofile-generate
> +export CFLAGS_PGO_CLANG
> +
>  CFLAGS_GCOV    := -fprofile-arcs -ftest-coverage \
>         $(call cc-option,-fno-tree-loop-im) \
>         $(call cc-disable-warning,maybe-uninitialized,)
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 78c6f05b10f91..a7a6ab7d204dc 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -1106,6 +1106,7 @@ config ARCH_SUPPORTS_DEBUG_PAGEALLOC
>         bool
>
>  source "kernel/gcov/Kconfig"
> +source "kernel/pgo/Kconfig"
>
>  source "scripts/gcc-plugins/Kconfig"
>
> diff --git a/arch/arm/boot/bootp/Makefile b/arch/arm/boot/bootp/Makefile
> index 981a8d03f064c..523bd58df0a4b 100644
> --- a/arch/arm/boot/bootp/Makefile
> +++ b/arch/arm/boot/bootp/Makefile
> @@ -7,6 +7,7 @@
>  #
>
>  GCOV_PROFILE   := n
> +PGO_PROFILE    := n
>
>  LDFLAGS_bootp  := --no-undefined -X \
>                  --defsym initrd_phys=$(INITRD_PHYS) \
> diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
> index fb521efcc6c20..5fd0fd85fc0e5 100644
> --- a/arch/arm/boot/compressed/Makefile
> +++ b/arch/arm/boot/compressed/Makefile
> @@ -24,6 +24,7 @@ OBJS          += hyp-stub.o
>  endif
>
>  GCOV_PROFILE           := n
> +PGO_PROFILE            := n
>  KASAN_SANITIZE         := n
>
>  # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
> diff --git a/arch/arm/vdso/Makefile b/arch/arm/vdso/Makefile
> index b558bee0e1f6b..11f6ce4b48b56 100644
> --- a/arch/arm/vdso/Makefile
> +++ b/arch/arm/vdso/Makefile
> @@ -36,8 +36,9 @@ else
>  CFLAGS_vgettimeofday.o = -O2 -include $(c-gettimeofday-y)
>  endif
>
> -# Disable gcov profiling for VDSO code
> +# Disable gcov and PGO profiling for VDSO code
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>
>  # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
>  KCOV_INSTRUMENT := n
> diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
> index cd9c3fa25902f..d48fc0df07020 100644
> --- a/arch/arm64/kernel/vdso/Makefile
> +++ b/arch/arm64/kernel/vdso/Makefile
> @@ -41,8 +41,9 @@ ifneq ($(c-gettimeofday-y),)
>    CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)
>  endif
>
> -# Disable gcov profiling for VDSO code
> +# Disable gcov and PGO profiling for VDSO code
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>
>  obj-y += vdso.o
>  targets += vdso.lds
> diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
> index 1f1e351c5fe2b..ad128ecdbfbdf 100644
> --- a/arch/arm64/kvm/hyp/nvhe/Makefile
> +++ b/arch/arm64/kvm/hyp/nvhe/Makefile
> @@ -60,6 +60,7 @@ KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS), $(KBUILD_CFLAG
>  # compiler instrumentation that inserts callbacks or checks into the code may
>  # cause crashes. Just disable it.
>  GCOV_PROFILE   := n
> +PGO_PROFILE    := n
>  KASAN_SANITIZE := n
>  UBSAN_SANITIZE := n
>  KCOV_INSTRUMENT        := n
> diff --git a/arch/mips/boot/compressed/Makefile b/arch/mips/boot/compressed/Makefile
> index 47cd9dc7454af..0855ea12f2c7f 100644
> --- a/arch/mips/boot/compressed/Makefile
> +++ b/arch/mips/boot/compressed/Makefile
> @@ -37,6 +37,7 @@ KBUILD_AFLAGS := $(KBUILD_AFLAGS) -D__ASSEMBLY__ \
>  # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
>  KCOV_INSTRUMENT                := n
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>
>  # decompressor objects (linked with vmlinuz)
>  vmlinuzobjs-y := $(obj)/head.o $(obj)/decompress.o $(obj)/string.o
> diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
> index 5810cc12bc1d9..d7eb64de35eae 100644
> --- a/arch/mips/vdso/Makefile
> +++ b/arch/mips/vdso/Makefile
> @@ -66,6 +66,7 @@ ldflags-y := -Bsymbolic --no-undefined -soname=linux-vdso.so.1 \
>  CFLAGS_REMOVE_vdso.o = -pg
>
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>  UBSAN_SANITIZE := n
>  KCOV_INSTRUMENT := n
>
> diff --git a/arch/nds32/kernel/vdso/Makefile b/arch/nds32/kernel/vdso/Makefile
> index 55df25ef00578..f2b53ee2124b7 100644
> --- a/arch/nds32/kernel/vdso/Makefile
> +++ b/arch/nds32/kernel/vdso/Makefile
> @@ -15,9 +15,9 @@ obj-vdso := $(addprefix $(obj)/, $(obj-vdso))
>  ccflags-y := -shared -fno-common -fno-builtin -nostdlib -fPIC -Wl,-shared -g \
>         -Wl,-soname=linux-vdso.so.1 -Wl,--hash-style=sysv
>
> -# Disable gcov profiling for VDSO code
> +# Disable gcov and PGO profiling for VDSO code
>  GCOV_PROFILE := n
> -
> +PGO_PROFILE := n
>
>  obj-y += vdso.o
>  targets += vdso.lds
> diff --git a/arch/parisc/boot/compressed/Makefile b/arch/parisc/boot/compressed/Makefile
> index dff4536875305..5cf93a67f7da7 100644
> --- a/arch/parisc/boot/compressed/Makefile
> +++ b/arch/parisc/boot/compressed/Makefile
> @@ -7,6 +7,7 @@
>
>  KCOV_INSTRUMENT := n
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>  UBSAN_SANITIZE := n
>
>  targets := vmlinux.lds vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index fe2ef598e2ead..c642c046660d7 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -153,17 +153,21 @@ endif
>  obj-$(CONFIG_PPC_SECURE_BOOT)  += secure_boot.o ima_arch.o secvar-ops.o
>  obj-$(CONFIG_PPC_SECVAR_SYSFS) += secvar-sysfs.o
>
> -# Disable GCOV, KCOV & sanitizers in odd or sensitive code
> +# Disable GCOV, PGO, KCOV & sanitizers in odd or sensitive code
>  GCOV_PROFILE_prom_init.o := n
> +PGO_PROFILE_prom_init.o := n
>  KCOV_INSTRUMENT_prom_init.o := n
>  UBSAN_SANITIZE_prom_init.o := n
>  GCOV_PROFILE_kprobes.o := n
> +PGO_PROFILE_kprobes.o := n
>  KCOV_INSTRUMENT_kprobes.o := n
>  UBSAN_SANITIZE_kprobes.o := n
>  GCOV_PROFILE_kprobes-ftrace.o := n
> +PGO_PROFILE_kprobes-ftrace.o := n
>  KCOV_INSTRUMENT_kprobes-ftrace.o := n
>  UBSAN_SANITIZE_kprobes-ftrace.o := n
>  GCOV_PROFILE_syscall_64.o := n
> +PGO_PROFILE_syscall_64.o := n
>  KCOV_INSTRUMENT_syscall_64.o := n
>  UBSAN_SANITIZE_syscall_64.o := n
>  UBSAN_SANITIZE_vdso.o := n
> diff --git a/arch/powerpc/kernel/trace/Makefile b/arch/powerpc/kernel/trace/Makefile
> index 858503775c583..7d72ae7d4f8c6 100644
> --- a/arch/powerpc/kernel/trace/Makefile
> +++ b/arch/powerpc/kernel/trace/Makefile
> @@ -23,7 +23,8 @@ obj-$(CONFIG_TRACING)                 += trace_clock.o
>  obj-$(CONFIG_PPC64)                    += $(obj64-y)
>  obj-$(CONFIG_PPC32)                    += $(obj32-y)
>
> -# Disable GCOV, KCOV & sanitizers in odd or sensitive code
> +# Disable GCOV, PGO, KCOV & sanitizers in odd or sensitive code
>  GCOV_PROFILE_ftrace.o := n
> +PGO_PROFILE_ftrace.o := n
>  KCOV_INSTRUMENT_ftrace.o := n
>  UBSAN_SANITIZE_ftrace.o := n
> diff --git a/arch/powerpc/kernel/vdso32/Makefile b/arch/powerpc/kernel/vdso32/Makefile
> index 9cb6f524854b9..655e159975a04 100644
> --- a/arch/powerpc/kernel/vdso32/Makefile
> +++ b/arch/powerpc/kernel/vdso32/Makefile
> @@ -34,6 +34,7 @@ targets := $(obj-vdso32) vdso32.so.dbg
>  obj-vdso32 := $(addprefix $(obj)/, $(obj-vdso32))
>
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>  KCOV_INSTRUMENT := n
>  UBSAN_SANITIZE := n
>  KASAN_SANITIZE := n
> diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile
> index bf363ff371521..12c286f5afc16 100644
> --- a/arch/powerpc/kernel/vdso64/Makefile
> +++ b/arch/powerpc/kernel/vdso64/Makefile
> @@ -21,6 +21,7 @@ targets := $(obj-vdso64) vdso64.so.dbg
>  obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64))
>
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>  KCOV_INSTRUMENT := n
>  UBSAN_SANITIZE := n
>  KASAN_SANITIZE := n
> diff --git a/arch/powerpc/kexec/Makefile b/arch/powerpc/kexec/Makefile
> index 4aff6846c7726..1c7f65e3cb969 100644
> --- a/arch/powerpc/kexec/Makefile
> +++ b/arch/powerpc/kexec/Makefile
> @@ -16,7 +16,8 @@ endif
>  endif
>
>
> -# Disable GCOV, KCOV & sanitizers in odd or sensitive code
> +# Disable GCOV, PGO, KCOV & sanitizers in odd or sensitive code
>  GCOV_PROFILE_core_$(BITS).o := n
> +PGO_PROFILE_core_$(BITS).o := n
>  KCOV_INSTRUMENT_core_$(BITS).o := n
>  UBSAN_SANITIZE_core_$(BITS).o := n
> diff --git a/arch/powerpc/xmon/Makefile b/arch/powerpc/xmon/Makefile
> index eb25d7554ffd1..7aff80d18b44b 100644
> --- a/arch/powerpc/xmon/Makefile
> +++ b/arch/powerpc/xmon/Makefile
> @@ -2,6 +2,7 @@
>  # Makefile for xmon
>
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>  KCOV_INSTRUMENT := n
>  UBSAN_SANITIZE := n
>  KASAN_SANITIZE := n
> diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
> index 0cfd6da784f84..882340dc3c647 100644
> --- a/arch/riscv/kernel/vdso/Makefile
> +++ b/arch/riscv/kernel/vdso/Makefile
> @@ -32,8 +32,9 @@ CPPFLAGS_vdso.lds += -P -C -U$(ARCH)
>  # Disable -pg to prevent insert call site
>  CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os
>
> -# Disable gcov profiling for VDSO code
> +# Disable gcov and PGO profiling for VDSO code
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>  KCOV_INSTRUMENT := n
>
>  # Force dependency
> diff --git a/arch/s390/boot/Makefile b/arch/s390/boot/Makefile
> index 41a64b8dce252..bee4a32040e79 100644
> --- a/arch/s390/boot/Makefile
> +++ b/arch/s390/boot/Makefile
> @@ -5,6 +5,7 @@
>
>  KCOV_INSTRUMENT := n
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>  UBSAN_SANITIZE := n
>  KASAN_SANITIZE := n
>
> diff --git a/arch/s390/boot/compressed/Makefile b/arch/s390/boot/compressed/Makefile
> index de18dab518bb6..c3ab883e8425a 100644
> --- a/arch/s390/boot/compressed/Makefile
> +++ b/arch/s390/boot/compressed/Makefile
> @@ -7,6 +7,7 @@
>
>  KCOV_INSTRUMENT := n
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>  UBSAN_SANITIZE := n
>  KASAN_SANITIZE := n
>
> diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile
> index dd73b7f074237..bd857aacad794 100644
> --- a/arch/s390/kernel/Makefile
> +++ b/arch/s390/kernel/Makefile
> @@ -14,6 +14,7 @@ CFLAGS_REMOVE_early.o         = $(CC_FLAGS_FTRACE)
>  endif
>
>  GCOV_PROFILE_early.o           := n
> +PGO_PROFILE_early.o            := n
>  KCOV_INSTRUMENT_early.o                := n
>  UBSAN_SANITIZE_early.o         := n
>  KASAN_SANITIZE_ipl.o           := n
> diff --git a/arch/s390/kernel/vdso64/Makefile b/arch/s390/kernel/vdso64/Makefile
> index a6e0fb6b91d6c..d7c43b7c1db96 100644
> --- a/arch/s390/kernel/vdso64/Makefile
> +++ b/arch/s390/kernel/vdso64/Makefile
> @@ -35,8 +35,9 @@ obj-y += vdso64_wrapper.o
>  targets += vdso64.lds
>  CPPFLAGS_vdso64.lds += -P -C -U$(ARCH)
>
> -# Disable gcov profiling, ubsan and kasan for VDSO code
> +# Disable gcov and PGO profiling, ubsan and kasan for VDSO code
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>  UBSAN_SANITIZE := n
>  KASAN_SANITIZE := n
>
> diff --git a/arch/s390/purgatory/Makefile b/arch/s390/purgatory/Makefile
> index c57f8c40e9926..9aef584e98466 100644
> --- a/arch/s390/purgatory/Makefile
> +++ b/arch/s390/purgatory/Makefile
> @@ -17,6 +17,7 @@ $(obj)/mem.o: $(srctree)/arch/s390/lib/mem.S FORCE
>
>  KCOV_INSTRUMENT := n
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>  UBSAN_SANITIZE := n
>  KASAN_SANITIZE := n
>
> diff --git a/arch/sh/boot/compressed/Makefile b/arch/sh/boot/compressed/Makefile
> index 589d2d8a573db..ae19aeeb3964c 100644
> --- a/arch/sh/boot/compressed/Makefile
> +++ b/arch/sh/boot/compressed/Makefile
> @@ -13,6 +13,7 @@ targets               := vmlinux vmlinux.bin vmlinux.bin.gz \
>  OBJECTS = $(obj)/head_32.o $(obj)/misc.o $(obj)/cache.o
>
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>
>  #
>  # IMAGE_OFFSET is the load offset of the compression loader
> diff --git a/arch/sh/mm/Makefile b/arch/sh/mm/Makefile
> index f69ddc70b1465..ea2782c631f43 100644
> --- a/arch/sh/mm/Makefile
> +++ b/arch/sh/mm/Makefile
> @@ -43,3 +43,4 @@ obj-$(CONFIG_UNCACHED_MAPPING)        += uncached.o
>  obj-$(CONFIG_HAVE_SRAM_POOL)   += sram.o
>
>  GCOV_PROFILE_pmb.o := n
> +PGO_PROFILE_pmb.o := n
> diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile
> index c5e1545bc5cf9..ab5f3783fe199 100644
> --- a/arch/sparc/vdso/Makefile
> +++ b/arch/sparc/vdso/Makefile
> @@ -115,6 +115,7 @@ quiet_cmd_vdso = VDSO    $@
>
>  VDSO_LDFLAGS = -shared --hash-style=both --build-id=sha1 -Bsymbolic
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>
>  #
>  # Install the unstripped copies of vdso*.so.  If our toolchain supports
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 7b6dd10b162ac..a751b4f8f6645 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -95,6 +95,7 @@ config X86
>         select ARCH_SUPPORTS_DEBUG_PAGEALLOC
>         select ARCH_SUPPORTS_NUMA_BALANCING     if X86_64
>         select ARCH_SUPPORTS_KMAP_LOCAL_FORCE_MAP       if NR_CPUS <= 4096
> +       select ARCH_SUPPORTS_PGO_CLANG          if X86_64
>         select ARCH_USE_BUILTIN_BSWAP
>         select ARCH_USE_QUEUED_RWLOCKS
>         select ARCH_USE_QUEUED_SPINLOCKS
> diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
> index fe605205b4ce2..383853e32f673 100644
> --- a/arch/x86/boot/Makefile
> +++ b/arch/x86/boot/Makefile
> @@ -71,6 +71,7 @@ KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
>  KBUILD_CFLAGS  += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
>  KBUILD_CFLAGS  += -fno-asynchronous-unwind-tables
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>  UBSAN_SANITIZE := n
>
>  $(obj)/bzImage: asflags-y  := $(SVGA_MODE)
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index e0bc3988c3faa..ed12ab65f6065 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -54,6 +54,7 @@ CFLAGS_sev-es.o += -I$(objtree)/arch/x86/lib/
>
>  KBUILD_AFLAGS  := $(KBUILD_CFLAGS) -D__ASSEMBLY__
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>  UBSAN_SANITIZE :=n
>
>  KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
> diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> index 02e3e42f380bd..26e2b3af0145c 100644
> --- a/arch/x86/entry/vdso/Makefile
> +++ b/arch/x86/entry/vdso/Makefile
> @@ -179,6 +179,7 @@ quiet_cmd_vdso = VDSO    $@
>  VDSO_LDFLAGS = -shared --hash-style=both --build-id=sha1 \
>         $(call ld-option, --eh-frame-hdr) -Bsymbolic
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>
>  quiet_cmd_vdso_and_check = VDSO    $@
>        cmd_vdso_and_check = $(cmd_vdso); $(cmd_vdso_check)
> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index efd9e9ea17f25..f6cab2316c46a 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -184,6 +184,8 @@ SECTIONS
>
>         BUG_TABLE
>
> +       PGO_CLANG_DATA
> +
>         ORC_UNWIND_TABLE
>
>         . = ALIGN(PAGE_SIZE);
> diff --git a/arch/x86/platform/efi/Makefile b/arch/x86/platform/efi/Makefile
> index 84b09c230cbd5..5f22b31446ad4 100644
> --- a/arch/x86/platform/efi/Makefile
> +++ b/arch/x86/platform/efi/Makefile
> @@ -2,6 +2,7 @@
>  OBJECT_FILES_NON_STANDARD_efi_thunk_$(BITS).o := y
>  KASAN_SANITIZE := n
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>
>  obj-$(CONFIG_EFI)              += quirks.o efi.o efi_$(BITS).o efi_stub_$(BITS).o
>  obj-$(CONFIG_EFI_MIXED)                += efi_thunk_$(BITS).o
> diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> index 95ea17a9d20cb..36f20e99da0bc 100644
> --- a/arch/x86/purgatory/Makefile
> +++ b/arch/x86/purgatory/Makefile
> @@ -23,6 +23,7 @@ targets += purgatory.ro purgatory.chk
>
>  # Sanitizer, etc. runtimes are unavailable and cannot be linked here.
>  GCOV_PROFILE   := n
> +PGO_PROFILE    := n
>  KASAN_SANITIZE := n
>  UBSAN_SANITIZE := n
>  KCSAN_SANITIZE := n
> diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile
> index 83f1b6a56449f..21797192f958f 100644
> --- a/arch/x86/realmode/rm/Makefile
> +++ b/arch/x86/realmode/rm/Makefile
> @@ -76,4 +76,5 @@ KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP -D_WAKEUP \
>  KBUILD_AFLAGS  := $(KBUILD_CFLAGS) -D__ASSEMBLY__
>  KBUILD_CFLAGS  += -fno-asynchronous-unwind-tables
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>  UBSAN_SANITIZE := n
> diff --git a/arch/x86/um/vdso/Makefile b/arch/x86/um/vdso/Makefile
> index 5943387e3f357..54f5768f58530 100644
> --- a/arch/x86/um/vdso/Makefile
> +++ b/arch/x86/um/vdso/Makefile
> @@ -64,6 +64,7 @@ quiet_cmd_vdso = VDSO    $@
>
>  VDSO_LDFLAGS = -fPIC -shared -Wl,--hash-style=sysv
>  GCOV_PROFILE := n
> +PGO_PROFILE := n
>
>  #
>  # Install the unstripped copy of vdso*.so listed in $(vdso-install-y).
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index 8a94388e38b33..2d81623b33f29 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -40,6 +40,7 @@ KBUILD_CFLAGS                 := $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
>  KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))
>
>  GCOV_PROFILE                   := n
> +PGO_PROFILE                    := n
>  # Sanitizer runtimes are unavailable and cannot be linked here.
>  KASAN_SANITIZE                 := n
>  KCSAN_SANITIZE                 := n
> diff --git a/drivers/s390/char/Makefile b/drivers/s390/char/Makefile
> index c6fdb81a068a6..bf6c5db5da1fc 100644
> --- a/drivers/s390/char/Makefile
> +++ b/drivers/s390/char/Makefile
> @@ -9,6 +9,7 @@ CFLAGS_REMOVE_sclp_early_core.o = $(CC_FLAGS_FTRACE)
>  endif
>
>  GCOV_PROFILE_sclp_early_core.o         := n
> +PGO_PROFILE_sclp_early_core.o          := n
>  KCOV_INSTRUMENT_sclp_early_core.o      := n
>  UBSAN_SANITIZE_sclp_early_core.o       := n
>  KASAN_SANITIZE_sclp_early_core.o       := n
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index b2b3d81b1535a..3a591bb18c5fb 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -316,6 +316,49 @@
>  #define THERMAL_TABLE(name)
>  #endif
>
> +#ifdef CONFIG_PGO_CLANG
> +#define PGO_CLANG_DATA                                                 \
> +       __llvm_prf_data : AT(ADDR(__llvm_prf_data) - LOAD_OFFSET) {     \
> +               . = ALIGN(8);                                           \
> +               __llvm_prf_start = .;                                   \
> +               __llvm_prf_data_start = .;                              \
> +               KEEP(*(__llvm_prf_data))                                \
> +               . = ALIGN(8);                                           \
> +               __llvm_prf_data_end = .;                                \
> +       }                                                               \
> +       __llvm_prf_cnts : AT(ADDR(__llvm_prf_cnts) - LOAD_OFFSET) {     \
> +               . = ALIGN(8);                                           \
> +               __llvm_prf_cnts_start = .;                              \
> +               KEEP(*(__llvm_prf_cnts))                                \
> +               . = ALIGN(8);                                           \
> +               __llvm_prf_cnts_end = .;                                \
> +       }                                                               \
> +       __llvm_prf_names : AT(ADDR(__llvm_prf_names) - LOAD_OFFSET) {   \
> +               . = ALIGN(8);                                           \
> +               __llvm_prf_names_start = .;                             \
> +               KEEP(*(__llvm_prf_names))                               \
> +               . = ALIGN(8);                                           \
> +               __llvm_prf_names_end = .;                               \
> +               . = ALIGN(8);                                           \
> +       }                                                               \
> +       __llvm_prf_vals : AT(ADDR(__llvm_prf_vals) - LOAD_OFFSET) {     \
> +               __llvm_prf_vals_start = .;                              \
> +               KEEP(*(__llvm_prf_vals))                                \
> +               . = ALIGN(8);                                           \
> +               __llvm_prf_vals_end = .;                                \
> +               . = ALIGN(8);                                           \
> +       }                                                               \
> +       __llvm_prf_vnds : AT(ADDR(__llvm_prf_vnds) - LOAD_OFFSET) {     \
> +               __llvm_prf_vnds_start = .;                              \
> +               KEEP(*(__llvm_prf_vnds))                                \
> +               . = ALIGN(8);                                           \
> +               __llvm_prf_vnds_end = .;                                \
> +               __llvm_prf_end = .;                                     \
> +       }
> +#else
> +#define PGO_CLANG_DATA
> +#endif
> +
>  #define KERNEL_DTB()                                                   \
>         STRUCT_ALIGN();                                                 \
>         __dtb_start = .;                                                \
> @@ -1125,6 +1168,7 @@
>                 CONSTRUCTORS                                            \
>         }                                                               \
>         BUG_TABLE                                                       \
> +       PGO_CLANG_DATA
>
>  #define INIT_TEXT_SECTION(inittext_align)                              \
>         . = ALIGN(inittext_align);                                      \
> diff --git a/kernel/Makefile b/kernel/Makefile
> index aa7368c7eabf3..0b34ca228ba46 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -111,6 +111,7 @@ obj-$(CONFIG_BPF) += bpf/
>  obj-$(CONFIG_KCSAN) += kcsan/
>  obj-$(CONFIG_SHADOW_CALL_STACK) += scs.o
>  obj-$(CONFIG_HAVE_STATIC_CALL_INLINE) += static_call.o
> +obj-$(CONFIG_PGO_CLANG) += pgo/
>
>  obj-$(CONFIG_PERF_EVENTS) += events/
>
> diff --git a/kernel/pgo/Kconfig b/kernel/pgo/Kconfig
> new file mode 100644
> index 0000000000000..318d36bb3d106
> --- /dev/null
> +++ b/kernel/pgo/Kconfig
> @@ -0,0 +1,34 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +menu "Profile Guided Optimization (PGO) (EXPERIMENTAL)"
> +
> +config ARCH_SUPPORTS_PGO_CLANG
> +       bool
> +
> +config PGO_CLANG
> +       bool "Enable clang's PGO-based kernel profiling"
> +       depends on DEBUG_FS
> +       depends on ARCH_SUPPORTS_PGO_CLANG
> +       help
> +         This option enables clang's PGO (Profile Guided Optimization) based
> +         code profiling to better optimize the kernel.
> +
> +         If unsure, say N.
> +
> +         Run a representative workload for your application on a kernel
> +         compiled with this option and download the raw profile file from
> +         /sys/kernel/debug/pgo/profraw. This file needs to be processed with
> +         llvm-profdata. It may be merged with other collected raw profiles.
> +
> +         Copy the resulting profile file into vmlinux.profdata, and enable
> +         KCFLAGS=-fprofile-use=vmlinux.profdata to produce an optimized
> +         kernel.
> +
> +         Note that a kernel compiled with profiling flags will be
> +         significatnly larger and run slower. Also be sure to exclude files
> +         from profiling which are not linked to the kernel image to prevent
> +         linker errors.
> +
> +         Note that the debugfs filesystem has to be mounted to access
> +         profiling data.
> +
> +endmenu
> diff --git a/kernel/pgo/Makefile b/kernel/pgo/Makefile
> new file mode 100644
> index 0000000000000..41e27cefd9a47
> --- /dev/null
> +++ b/kernel/pgo/Makefile
> @@ -0,0 +1,5 @@
> +# SPDX-License-Identifier: GPL-2.0
> +GCOV_PROFILE   := n
> +PGO_PROFILE    := n
> +
> +obj-y  += fs.o instrument.o
> diff --git a/kernel/pgo/fs.c b/kernel/pgo/fs.c
> new file mode 100644
> index 0000000000000..790a8df037bfc
> --- /dev/null
> +++ b/kernel/pgo/fs.c
> @@ -0,0 +1,382 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2019 Google, Inc.
> + *
> + * Author:
> + *     Sami Tolvanen <samitolvanen@google.com>
> + *
> + * This software is licensed under the terms of the GNU General Public
> + * License version 2, as published by the Free Software Foundation, and
> + * may be copied, distributed, and modified under those terms.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + */
> +
> +#define pr_fmt(fmt)    "pgo: " fmt
> +
> +#include <linux/kernel.h>
> +#include <linux/debugfs.h>
> +#include <linux/fs.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/vmalloc.h>
> +#include "pgo.h"
> +
> +static struct dentry *directory;
> +
> +struct prf_private_data {
> +       void *buffer;
> +       unsigned long size;
> +};
> +
> +/*
> + * Raw profile data format:
> + *
> + *     - llvm_prf_header
> + *     - __llvm_prf_data
> + *     - __llvm_prf_cnts
> + *     - __llvm_prf_names
> + *     - zero padding to 8 bytes
> + *     - for each llvm_prf_data in __llvm_prf_data:
> + *             - llvm_prf_value_data
> + *                     - llvm_prf_value_record + site count array
> + *                             - llvm_prf_value_node_data
> + *                             ...
> + *                     ...
> + *             ...
> + */
> +
> +static void prf_fill_header(void **buffer)
> +{
> +       struct llvm_prf_header *header = *(struct llvm_prf_header **)buffer;
> +
> +       header->magic = LLVM_PRF_MAGIC;
> +       header->version = LLVM_PRF_VARIANT_MASK_IR | LLVM_PRF_VERSION;
> +       header->data_size = prf_data_count();
> +       header->padding_bytes_before_counters = 0;
> +       header->counters_size = prf_cnts_count();
> +       header->padding_bytes_after_counters = 0;
> +       header->names_size = prf_names_count();
> +       header->counters_delta = (u64)__llvm_prf_cnts_start;
> +       header->names_delta = (u64)__llvm_prf_names_start;
> +       header->value_kind_last = LLVM_PRF_IPVK_LAST;
> +
> +       *buffer += sizeof(*header);
> +}
> +
> +/*
> + * Copy the source into the buffer, incrementing the pointer into buffer in the
> + * process.
> + */
> +static void prf_copy_to_buffer(void **buffer, void *src, unsigned long size)
> +{
> +       memcpy(*buffer, src, size);
> +       *buffer += size;
> +}
> +
> +static u32 __prf_get_value_size(struct llvm_prf_data *p, u32 *value_kinds)
> +{
> +       struct llvm_prf_value_node **nodes =
> +               (struct llvm_prf_value_node **)p->values;
> +       u32 kinds = 0;
> +       u32 size = 0;
> +       unsigned int kind;
> +       unsigned int n;
> +       unsigned int s = 0;
> +
> +       for (kind = 0; kind < ARRAY_SIZE(p->num_value_sites); kind++) {
> +               unsigned int sites = p->num_value_sites[kind];
> +
> +               if (!sites)
> +                       continue;
> +
> +               /* Record + site count array */
> +               size += prf_get_value_record_size(sites);
> +               kinds++;
> +
> +               if (!nodes)
> +                       continue;
> +
> +               for (n = 0; n < sites; n++) {
> +                       u32 count = 0;
> +                       struct llvm_prf_value_node *site = nodes[s + n];
> +
> +                       while (site && ++count <= U8_MAX)
> +                               site = site->next;
> +
> +                       size += count *
> +                               sizeof(struct llvm_prf_value_node_data);
> +               }
> +
> +               s += sites;
> +       }
> +
> +       if (size)
> +               size += sizeof(struct llvm_prf_value_data);
> +
> +       if (value_kinds)
> +               *value_kinds = kinds;
> +
> +       return size;
> +}
> +
> +static u32 prf_get_value_size(void)
> +{
> +       u32 size = 0;
> +       struct llvm_prf_data *p;
> +
> +       for (p = __llvm_prf_data_start; p < __llvm_prf_data_end; p++)
> +               size += __prf_get_value_size(p, NULL);
> +
> +       return size;
> +}
> +
> +/* Serialize the profiling's value. */
> +static void prf_serialize_value(struct llvm_prf_data *p, void **buffer)
> +{
> +       struct llvm_prf_value_data header;
> +       struct llvm_prf_value_node **nodes =
> +               (struct llvm_prf_value_node **)p->values;
> +       unsigned int kind;
> +       unsigned int n;
> +       unsigned int s = 0;
> +
> +       header.total_size = __prf_get_value_size(p, &header.num_value_kinds);
> +
> +       if (!header.num_value_kinds)
> +               /* Nothing to write. */
> +               return;
> +
> +       prf_copy_to_buffer(buffer, &header, sizeof(header));
> +
> +       for (kind = 0; kind < ARRAY_SIZE(p->num_value_sites); kind++) {
> +               struct llvm_prf_value_record *record;
> +               u8 *counts;
> +               unsigned int sites = p->num_value_sites[kind];
> +
> +               if (!sites)
> +                       continue;
> +
> +               /* Profiling value record. */
> +               record = *(struct llvm_prf_value_record **)buffer;
> +               *buffer += prf_get_value_record_header_size();
> +
> +               record->kind = kind;
> +               record->num_value_sites = sites;
> +
> +               /* Site count array. */
> +               counts = *(u8 **)buffer;
> +               *buffer += prf_get_value_record_site_count_size(sites);
> +
> +               /*
> +                * If we don't have nodes, we can skip updating the site count
> +                * array, because the buffer is zero filled.
> +                */
> +               if (!nodes)
> +                       continue;
> +
> +               for (n = 0; n < sites; n++) {
> +                       u32 count = 0;
> +                       struct llvm_prf_value_node *site = nodes[s + n];
> +
> +                       while (site && ++count <= U8_MAX) {
> +                               prf_copy_to_buffer(buffer, site,
> +                                                  sizeof(struct llvm_prf_value_node_data));
> +                               site = site->next;
> +                       }
> +
> +                       counts[n] = (u8)count;
> +               }
> +
> +               s += sites;
> +       }
> +}
> +
> +static void prf_serialize_values(void **buffer)
> +{
> +       struct llvm_prf_data *p;
> +
> +       for (p = __llvm_prf_data_start; p < __llvm_prf_data_end; p++)
> +               prf_serialize_value(p, buffer);
> +}
> +
> +static inline unsigned long prf_get_padding(unsigned long size)
> +{
> +       return 8 - (size % 8);
> +}
> +
> +static unsigned long prf_buffer_size(void)
> +{
> +       return sizeof(struct llvm_prf_header) +
> +                       prf_data_size() +
> +                       prf_cnts_size() +
> +                       prf_names_size() +
> +                       prf_get_padding(prf_names_size()) +
> +                       prf_get_value_size();
> +}
> +
> +/* Serialize the profling data into a format LLVM's tools can understand. */
> +static int prf_serialize(struct prf_private_data *p)
> +{
> +       int err = 0;
> +       void *buffer;
> +
> +       p->size = prf_buffer_size();
> +       p->buffer = vzalloc(p->size);
> +
> +       if (!p->buffer) {
> +               err = -ENOMEM;
> +               goto out;
> +       }
> +
> +       buffer = p->buffer;
> +
> +       prf_fill_header(&buffer);
> +       prf_copy_to_buffer(&buffer, __llvm_prf_data_start,  prf_data_size());
> +       prf_copy_to_buffer(&buffer, __llvm_prf_cnts_start,  prf_cnts_size());
> +       prf_copy_to_buffer(&buffer, __llvm_prf_names_start, prf_names_size());
> +       buffer += prf_get_padding(prf_names_size());
> +
> +       prf_serialize_values(&buffer);
> +
> +out:
> +       return err;
> +}
> +
> +/* open() implementation for PGO. Creates a copy of the profiling data set. */
> +static int prf_open(struct inode *inode, struct file *file)
> +{
> +       struct prf_private_data *data;
> +       unsigned long flags;
> +       int err;
> +
> +       data = kzalloc(sizeof(*data), GFP_KERNEL);
> +       if (!data) {
> +               err = -ENOMEM;
> +               goto out;
> +       }
> +
> +       flags = prf_lock();
> +
> +       err = prf_serialize(data);
> +       if (err) {
> +               kfree(data);
> +               goto out_unlock;
> +       }
> +
> +       file->private_data = data;
> +
> +out_unlock:
> +       prf_unlock(flags);
> +out:
> +       return err;
> +}
> +
> +/* read() implementation for PGO. */
> +static ssize_t prf_read(struct file *file, char __user *buf, size_t count,
> +                       loff_t *ppos)
> +{
> +       struct prf_private_data *data = file->private_data;
> +
> +       BUG_ON(!data);
> +
> +       return simple_read_from_buffer(buf, count, ppos, data->buffer,
> +                                      data->size);
> +}
> +
> +/* release() implementation for PGO. Release resources allocated by open(). */
> +static int prf_release(struct inode *inode, struct file *file)
> +{
> +       struct prf_private_data *data = file->private_data;
> +
> +       if (data) {
> +               vfree(data->buffer);
> +               kfree(data);
> +       }
> +
> +       return 0;
> +}
> +
> +static const struct file_operations prf_fops = {
> +       .owner          = THIS_MODULE,
> +       .open           = prf_open,
> +       .read           = prf_read,
> +       .llseek         = default_llseek,
> +       .release        = prf_release
> +};
> +
> +/* write() implementation for resetting PGO's profile data. */
> +static ssize_t reset_write(struct file *file, const char __user *addr,
> +                          size_t len, loff_t *pos)
> +{
> +       struct llvm_prf_data *data;
> +
> +       memset(__llvm_prf_cnts_start, 0, prf_cnts_size());
> +
> +       for (data = __llvm_prf_data_start; data < __llvm_prf_data_end; ++data) {
> +               struct llvm_prf_value_node **vnodes;
> +               u64 current_vsite_count;
> +               u32 i;
> +
> +               if (!data->values)
> +                       continue;
> +
> +               current_vsite_count = 0;
> +               vnodes = (struct llvm_prf_value_node **)data->values;
> +
> +               for (i = LLVM_PRF_IPVK_FIRST; i <= LLVM_PRF_IPVK_LAST; ++i)
> +                       current_vsite_count += data->num_value_sites[i];
> +
> +               for (i = 0; i < current_vsite_count; ++i) {
> +                       struct llvm_prf_value_node *current_vnode = vnodes[i];
> +
> +                       while (current_vnode) {
> +                               current_vnode->count = 0;
> +                               current_vnode = current_vnode->next;
> +                       }
> +               }
> +       }
> +
> +       return len;
> +}
> +
> +static const struct file_operations prf_reset_fops = {
> +       .owner          = THIS_MODULE,
> +       .write          = reset_write,
> +       .llseek         = noop_llseek,
> +};
> +
> +/* Create debugfs entries. */
> +static int __init pgo_init(void)
> +{
> +       directory = debugfs_create_dir("pgo", NULL);
> +       if (!directory)
> +               goto err_remove;
> +
> +       if (!debugfs_create_file("profraw", 0600, directory, NULL,
> +                                &prf_fops))
> +               goto err_remove;
> +
> +       if (!debugfs_create_file("reset", 0200, directory, NULL,
> +                                &prf_reset_fops))
> +               goto err_remove;
> +
> +       return 0;
> +
> +err_remove:
> +       pr_err("initialization failed\n");
> +       return -EIO;
> +}
> +
> +/* Remove debufs entries. */
> +static void __exit pgo_exit(void)
> +{
> +       debugfs_remove_recursive(directory);
> +}
> +
> +module_init(pgo_init);
> +module_exit(pgo_exit);
> diff --git a/kernel/pgo/instrument.c b/kernel/pgo/instrument.c
> new file mode 100644
> index 0000000000000..d96b61a1cf712
> --- /dev/null
> +++ b/kernel/pgo/instrument.c
> @@ -0,0 +1,147 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2019 Google, Inc.
> + *
> + * Author:
> + *     Sami Tolvanen <samitolvanen@google.com>
> + *
> + * This software is licensed under the terms of the GNU General Public
> + * License version 2, as published by the Free Software Foundation, and
> + * may be copied, distributed, and modified under those terms.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + */
> +
> +#define pr_fmt(fmt)    "pgo: " fmt
> +
> +#include <linux/kernel.h>
> +#include <linux/export.h>
> +#include <linux/spinlock.h>
> +#include <linux/types.h>
> +#include "pgo.h"
> +
> +/* Lock guarding value node access and serialization. */
> +static DEFINE_SPINLOCK(pgo_lock);
> +static int current_node;
> +
> +unsigned long prf_lock(void)
> +{
> +       unsigned long flags;
> +
> +       spin_lock_irqsave(&pgo_lock, flags);
> +
> +       return flags;
> +}
> +
> +void prf_unlock(unsigned long flags)
> +{
> +       spin_unlock_irqrestore(&pgo_lock, flags);
> +}
> +
> +/*
> + * Return a newly allocated profiling value node which contains the tracked
> + * value by the value profiler.
> + * Note: caller *must* hold pgo_lock.
> + */
> +static struct llvm_prf_value_node *allocate_node(struct llvm_prf_data *p,
> +                                                u32 index, u64 value)
> +{
> +       if (&__llvm_prf_vnds_start[current_node + 1] >= __llvm_prf_vnds_end)
> +               return NULL; /* Out of nodes */
> +
> +       current_node++;
> +
> +       /* Make sure the node is entirely within the section */
> +       if (&__llvm_prf_vnds_start[current_node] >= __llvm_prf_vnds_end ||
> +           &__llvm_prf_vnds_start[current_node + 1] > __llvm_prf_vnds_end)
> +               return NULL;
> +
> +       return &__llvm_prf_vnds_start[current_node];
> +}
> +
> +/*
> + * Counts the number of times a target value is seen.
> + *
> + * Records the target value for the CounterIndex if not seen before. Otherwise,
> + * increments the counter associated w/ the target value.
> + */
> +void __llvm_profile_instrument_target(u64 target_value, void *data, u32 index)
> +{
> +       struct llvm_prf_data *p = (struct llvm_prf_data *)data;
> +       struct llvm_prf_value_node **counters;
> +       struct llvm_prf_value_node *curr;
> +       struct llvm_prf_value_node *min = NULL;
> +       struct llvm_prf_value_node *prev = NULL;
> +       u64 min_count = U64_MAX;
> +       u8 values = 0;
> +       unsigned long flags;
> +
> +       if (!p || !p->values)
> +               return;
> +
> +       counters = (struct llvm_prf_value_node **)p->values;
> +       curr = counters[index];
> +
> +       while (curr) {
> +               if (target_value == curr->value) {
> +                       curr->count++;
> +                       return;
> +               }
> +
> +               if (curr->count < min_count) {
> +                       min_count = curr->count;
> +                       min = curr;
> +               }
> +
> +               prev = curr;
> +               curr = curr->next;
> +               values++;
> +       }
> +
> +       if (values >= LLVM_PRF_MAX_NUM_VALS_PER_SITE) {
> +               if (!min->count || !(--min->count)) {
> +                       curr = min;
> +                       curr->value = target_value;
> +                       curr->count++;
> +               }
> +               return;
> +       }
> +
> +       /* Lock when updating the value node structure. */
> +       flags = prf_lock();
> +
> +       curr = allocate_node(p, index, target_value);
> +       if (!curr)
> +               goto out;
> +
> +       curr->value = target_value;
> +       curr->count++;
> +
> +       if (!counters[index])
> +               counters[index] = curr;
> +       else if (prev && !prev->next)
> +               prev->next = curr;
> +
> +out:
> +       prf_unlock(flags);
> +}
> +EXPORT_SYMBOL(__llvm_profile_instrument_target);
> +
> +/* Counts the number of times a range of targets values are seen. */
> +void __llvm_profile_instrument_range(u64 target_value, void *data,
> +                                    u32 index, s64 precise_start,
> +                                    s64 precise_last, s64 large_value)
> +{
> +       if (large_value != S64_MIN && (s64)target_value >= large_value)
> +               target_value = large_value;
> +       else if ((s64)target_value < precise_start ||
> +                (s64)target_value > precise_last)
> +               target_value = precise_last + 1;
> +
> +       __llvm_profile_instrument_target(target_value, data, index);
> +}
> +EXPORT_SYMBOL(__llvm_profile_instrument_range);
> diff --git a/kernel/pgo/pgo.h b/kernel/pgo/pgo.h
> new file mode 100644
> index 0000000000000..df0aa278f28bd
> --- /dev/null
> +++ b/kernel/pgo/pgo.h
> @@ -0,0 +1,206 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2019 Google, Inc.
> + *
> + * Author:
> + *     Sami Tolvanen <samitolvanen@google.com>
> + *
> + * This software is licensed under the terms of the GNU General Public
> + * License version 2, as published by the Free Software Foundation, and
> + * may be copied, distributed, and modified under those terms.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + */
> +
> +#ifndef _PGO_H
> +#define _PGO_H
> +
> +/*
> + * Note: These internal LLVM definitions must match the compiler version.
> + * See llvm/include/llvm/ProfileData/InstrProfData.inc in LLVM's source code.
> + */
> +
> +#ifdef CONFIG_64BIT
> +       #define LLVM_PRF_MAGIC          \
> +               ((u64)255 << 56 |       \
> +                (u64)'l' << 48 |       \
> +                (u64)'p' << 40 |       \
> +                (u64)'r' << 32 |       \
> +                (u64)'o' << 24 |       \
> +                (u64)'f' << 16 |       \
> +                (u64)'r' << 8  |       \
> +                (u64)129)
> +#else
> +       #define LLVM_PRF_MAGIC          \
> +               ((u64)255 << 56 |       \
> +                (u64)'l' << 48 |       \
> +                (u64)'p' << 40 |       \
> +                (u64)'r' << 32 |       \
> +                (u64)'o' << 24 |       \
> +                (u64)'f' << 16 |       \
> +                (u64)'R' << 8  |       \
> +                (u64)129)
> +#endif
> +
> +#define LLVM_PRF_VERSION               5
> +#define LLVM_PRF_DATA_ALIGN            8
> +#define LLVM_PRF_IPVK_FIRST            0
> +#define LLVM_PRF_IPVK_LAST             1
> +#define LLVM_PRF_MAX_NUM_VALS_PER_SITE 16
> +
> +#define LLVM_PRF_VARIANT_MASK_IR       (0x1ull << 56)
> +#define LLVM_PRF_VARIANT_MASK_CSIR     (0x1ull << 57)
> +
> +/**
> + * struct llvm_prf_header - represents the raw profile header data structure.
> + * @magic: the magic token for the file format.
> + * @version: the version of the file format.
> + * @data_size: the number of entries in the profile data section.
> + * @padding_bytes_before_counters: the number of padding bytes before the
> + *   counters.
> + * @counters_size: the size in bytes of the LLVM profile section containing the
> + *   counters.
> + * @padding_bytes_after_counters: the number of padding bytes after the
> + *   counters.
> + * @names_size: the size in bytes of the LLVM profile section containing the
> + *   counters' names.
> + * @counters_delta: the beginning of the LLMV profile counters section.
> + * @names_delta: the beginning of the LLMV profile names section.
> + * @value_kind_last: the last profile value kind.
> + */
> +struct llvm_prf_header {
> +       u64 magic;
> +       u64 version;
> +       u64 data_size;
> +       u64 padding_bytes_before_counters;
> +       u64 counters_size;
> +       u64 padding_bytes_after_counters;
> +       u64 names_size;
> +       u64 counters_delta;
> +       u64 names_delta;
> +       u64 value_kind_last;
> +};
> +
> +/**
> + * struct llvm_prf_data - represents the per-function control structure.
> + * @name_ref: the reference to the function's name.
> + * @func_hash: the hash value of the function.
> + * @counter_ptr: a pointer to the profile counter.
> + * @function_ptr: a pointer to the function.
> + * @values: the profiling values associated with this function.
> + * @num_counters: the number of counters in the function.
> + * @num_value_sites: the number of value profile sites.
> + */
> +struct llvm_prf_data {
> +       const u64 name_ref;
> +       const u64 func_hash;
> +       const void *counter_ptr;
> +       const void *function_ptr;
> +       void *values;
> +       const u32 num_counters;
> +       const u16 num_value_sites[LLVM_PRF_IPVK_LAST + 1];
> +} __aligned(LLVM_PRF_DATA_ALIGN);
> +
> +/**
> + * structure llvm_prf_value_node_data - represents the data part of the struct
> + *   llvm_prf_value_node data structure.
> + * @value: the value counters.
> + * @count: the counters' count.
> + */
> +struct llvm_prf_value_node_data {
> +       u64 value;
> +       u64 count;
> +};
> +
> +/**
> + * struct llvm_prf_value_node - represents an internal data structure used by
> + *   the value profiler.
> + * @value: the value counters.
> + * @count: the counters' count.
> + * @next: the next value node.
> + */
> +struct llvm_prf_value_node {
> +       u64 value;
> +       u64 count;
> +       struct llvm_prf_value_node *next;
> +};
> +
> +/**
> + * struct llvm_prf_value_data - represents the value profiling data in indexed
> + *   format.
> + * @total_size: the total size in bytes including this field.
> + * @num_value_kinds: the number of value profile kinds that has value profile
> + *   data.
> + */
> +struct llvm_prf_value_data {
> +       u32 total_size;
> +       u32 num_value_kinds;
> +};
> +
> +/**
> + * struct llvm_prf_value_record - represents the on-disk layout of the value
> + *   profile data of a particular kind for one function.
> + * @kind: the kind of the value profile record.
> + * @num_value_sites: the number of value profile sites.
> + * @site_count_array: the first element of the array that stores the number
> + *   of profiled values for each value site.
> + */
> +struct llvm_prf_value_record {
> +       u32 kind;
> +       u32 num_value_sites;
> +       u8 site_count_array[];
> +};
> +
> +#define prf_get_value_record_header_size()             \
> +       offsetof(struct llvm_prf_value_record, site_count_array)
> +#define prf_get_value_record_site_count_size(sites)    \
> +       roundup((sites), 8)
> +#define prf_get_value_record_size(sites)               \
> +       (prf_get_value_record_header_size() +           \
> +        prf_get_value_record_site_count_size((sites)))
> +
> +/* Data sections */
> +extern struct llvm_prf_data __llvm_prf_data_start[];
> +extern struct llvm_prf_data __llvm_prf_data_end[];
> +
> +extern u64 __llvm_prf_cnts_start[];
> +extern u64 __llvm_prf_cnts_end[];
> +
> +extern char __llvm_prf_names_start[];
> +extern char __llvm_prf_names_end[];
> +
> +extern struct llvm_prf_value_node __llvm_prf_vnds_start[];
> +extern struct llvm_prf_value_node __llvm_prf_vnds_end[];
> +
> +/* Locking for vnodes */
> +extern unsigned long prf_lock(void);
> +extern void prf_unlock(unsigned long flags);
> +
> +#define __DEFINE_PRF_SIZE(s) \
> +       static inline unsigned long prf_ ## s ## _size(void)            \
> +       {                                                               \
> +               unsigned long start =                                   \
> +                       (unsigned long)__llvm_prf_ ## s ## _start;      \
> +               unsigned long end =                                     \
> +                       (unsigned long)__llvm_prf_ ## s ## _end;        \
> +               return roundup(end - start,                             \
> +                               sizeof(__llvm_prf_ ## s ## _start[0])); \
> +       }                                                               \
> +       static inline unsigned long prf_ ## s ## _count(void)           \
> +       {                                                               \
> +               return prf_ ## s ## _size() /                           \
> +                       sizeof(__llvm_prf_ ## s ## _start[0]);          \
> +       }
> +
> +__DEFINE_PRF_SIZE(data);
> +__DEFINE_PRF_SIZE(cnts);
> +__DEFINE_PRF_SIZE(names);
> +__DEFINE_PRF_SIZE(vnds);
> +
> +#undef __DEFINE_PRF_SIZE
> +
> +#endif /* _PGO_H */
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index 213677a5ed33e..9b218afb5cb87 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -143,6 +143,16 @@ _c_flags += $(if $(patsubst n%,, \
>                 $(CFLAGS_GCOV))
>  endif
>
> +#
> +# Enable clang's PGO profiling flags for a file or directory depending on
> +# variables PGO_PROFILE_obj.o and PGO_PROFILE.
> +#
> +ifeq ($(CONFIG_PGO_CLANG),y)
> +_c_flags += $(if $(patsubst n%,, \
> +               $(PGO_PROFILE_$(basetarget).o)$(PGO_PROFILE)y), \
> +               $(CFLAGS_PGO_CLANG))
> +endif
> +
>  #
>  # Enable address sanitizer flags for kernel except some files or directories
>  # we don't want to check (depends on variables KASAN_SANITIZE_obj.o, KASAN_SANITIZE)
> --
> 2.30.0.284.gd98b1dd5eaa7-goog
>
> --
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Sedat Dilek Jan. 11, 2021, 8:42 a.m. UTC | #2
On Mon, Jan 11, 2021 at 9:39 AM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Mon, Jan 11, 2021 at 9:18 AM 'Bill Wendling' via Clang Built Linux
> <clang-built-linux@googlegroups.com> wrote:
> >
> > From: Sami Tolvanen <samitolvanen@google.com>
> >
> > Enable the use of clang's Profile-Guided Optimization[1]. To generate a
> > profile, the kernel is instrumented with PGO counters, a representative
> > workload is run, and the raw profile data is collected from
> > /sys/kernel/debug/pgo/profraw.
> >
> > The raw profile data must be processed by clang's "llvm-profdata" tool before
> > it can be used during recompilation:
> >
> >   $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
> >   $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> >
> > Multiple raw profiles may be merged during this step.
> >
> > The data can be used either by the compiler if LTO isn't enabled:
> >
> >     ... -fprofile-use=vmlinux.profdata ...
> >
> > or by LLD if LTO is enabled:
> >
> >     ... -lto-cs-profile-file=vmlinux.profdata ...
> >
> > This initial submission is restricted to x86, as that's the platform we know
> > works. This restriction can be lifted once other platforms have been verified
> > to work with PGO.
> >
> > Note that this method of profiling the kernel is clang-native and isn't
> > compatible with clang's gcov support in kernel/gcov.
> >
> > [1] https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
> >
>
> Hi Bill and Sami,
>
> I have seen the pull-request in the CBL issue tracker and had some
> questions in mind.
>
> Good you send this.
>
> First of all, I like to fetch any development stuff easily from a Git
> repository.
> Can you offer this, please?
> What is the base for your work?
> I hope this is (fresh released) Linux v5.11-rc3.
>
> I myself had some experiences with a PGO + ThinLTO optimized LLVM
> toolchain built with the help of tc-build.
> Here it takes very long to build it.
>
> This means I have some profile-data archived.
> Can I use it?
>
> Is an own PGO + ThinLTO optimized LLVM toolchain pre-requirement for
> this or not?

When I recall correctly such an optimized LLVM toolchain saved here
40% of build-time.
So, I am highly interested in reducing my build-time.

- Sedat -

> That is one of my important questions.
>
> Thanks for your work.
>
> Regards,
> - Sedat -
>
> > Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> > Co-developed-by: Bill Wendling <morbo@google.com>
> > Signed-off-by: Bill Wendling <morbo@google.com>
> > ---
> >  Documentation/dev-tools/index.rst     |   1 +
> >  Documentation/dev-tools/pgo.rst       | 127 +++++++++
> >  MAINTAINERS                           |   9 +
> >  Makefile                              |   3 +
> >  arch/Kconfig                          |   1 +
> >  arch/arm/boot/bootp/Makefile          |   1 +
> >  arch/arm/boot/compressed/Makefile     |   1 +
> >  arch/arm/vdso/Makefile                |   3 +-
> >  arch/arm64/kernel/vdso/Makefile       |   3 +-
> >  arch/arm64/kvm/hyp/nvhe/Makefile      |   1 +
> >  arch/mips/boot/compressed/Makefile    |   1 +
> >  arch/mips/vdso/Makefile               |   1 +
> >  arch/nds32/kernel/vdso/Makefile       |   4 +-
> >  arch/parisc/boot/compressed/Makefile  |   1 +
> >  arch/powerpc/kernel/Makefile          |   6 +-
> >  arch/powerpc/kernel/trace/Makefile    |   3 +-
> >  arch/powerpc/kernel/vdso32/Makefile   |   1 +
> >  arch/powerpc/kernel/vdso64/Makefile   |   1 +
> >  arch/powerpc/kexec/Makefile           |   3 +-
> >  arch/powerpc/xmon/Makefile            |   1 +
> >  arch/riscv/kernel/vdso/Makefile       |   3 +-
> >  arch/s390/boot/Makefile               |   1 +
> >  arch/s390/boot/compressed/Makefile    |   1 +
> >  arch/s390/kernel/Makefile             |   1 +
> >  arch/s390/kernel/vdso64/Makefile      |   3 +-
> >  arch/s390/purgatory/Makefile          |   1 +
> >  arch/sh/boot/compressed/Makefile      |   1 +
> >  arch/sh/mm/Makefile                   |   1 +
> >  arch/sparc/vdso/Makefile              |   1 +
> >  arch/x86/Kconfig                      |   1 +
> >  arch/x86/boot/Makefile                |   1 +
> >  arch/x86/boot/compressed/Makefile     |   1 +
> >  arch/x86/entry/vdso/Makefile          |   1 +
> >  arch/x86/kernel/vmlinux.lds.S         |   2 +
> >  arch/x86/platform/efi/Makefile        |   1 +
> >  arch/x86/purgatory/Makefile           |   1 +
> >  arch/x86/realmode/rm/Makefile         |   1 +
> >  arch/x86/um/vdso/Makefile             |   1 +
> >  drivers/firmware/efi/libstub/Makefile |   1 +
> >  drivers/s390/char/Makefile            |   1 +
> >  include/asm-generic/vmlinux.lds.h     |  44 +++
> >  kernel/Makefile                       |   1 +
> >  kernel/pgo/Kconfig                    |  34 +++
> >  kernel/pgo/Makefile                   |   5 +
> >  kernel/pgo/fs.c                       | 382 ++++++++++++++++++++++++++
> >  kernel/pgo/instrument.c               | 147 ++++++++++
> >  kernel/pgo/pgo.h                      | 206 ++++++++++++++
> >  scripts/Makefile.lib                  |  10 +
> >  48 files changed, 1017 insertions(+), 9 deletions(-)
> >  create mode 100644 Documentation/dev-tools/pgo.rst
> >  create mode 100644 kernel/pgo/Kconfig
> >  create mode 100644 kernel/pgo/Makefile
> >  create mode 100644 kernel/pgo/fs.c
> >  create mode 100644 kernel/pgo/instrument.c
> >  create mode 100644 kernel/pgo/pgo.h
> >
> > diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst
> > index f7809c7b1ba9e..8d6418e858062 100644
> > --- a/Documentation/dev-tools/index.rst
> > +++ b/Documentation/dev-tools/index.rst
> > @@ -26,6 +26,7 @@ whole; patches welcome!
> >     kgdb
> >     kselftest
> >     kunit/index
> > +   pgo
> >
> >
> >  .. only::  subproject and html
> > diff --git a/Documentation/dev-tools/pgo.rst b/Documentation/dev-tools/pgo.rst
> > new file mode 100644
> > index 0000000000000..2ed7f549b20ef
> > --- /dev/null
> > +++ b/Documentation/dev-tools/pgo.rst
> > @@ -0,0 +1,127 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +===============================
> > +Using PGO with the Linux kernel
> > +===============================
> > +
> > +Clang's profiling kernel support (PGO_) enables profiling of the Linux kernel
> > +when building with Clang. The profiling data is exported via the ``pgo``
> > +debugfs directory.
> > +
> > +.. _PGO: https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
> > +
> > +
> > +Preparation
> > +===========
> > +
> > +Configure the kernel with:
> > +
> > +.. code-block:: make
> > +
> > +   CONFIG_DEBUG_FS=y
> > +   CONFIG_PGO_CLANG=y
> > +
> > +Note that kernels compiled with profiling flags will be significantly larger
> > +and run slower.
> > +
> > +Profiling data will only become accessible once debugfs has been mounted:
> > +
> > +.. code-block:: sh
> > +
> > +   mount -t debugfs none /sys/kernel/debug
> > +
> > +
> > +Customization
> > +=============
> > +
> > +You can enable or disable profiling for individual file and directories by
> > +adding a line similar to the following to the respective kernel Makefile:
> > +
> > +- For a single file (e.g. main.o)
> > +
> > +  .. code-block:: make
> > +
> > +     PGO_PROFILE_main.o := y
> > +
> > +- For all files in one directory
> > +
> > +  .. code-block:: make
> > +
> > +     PGO_PROFILE := y
> > +
> > +To exclude files from being profiled use
> > +
> > +  .. code-block:: make
> > +
> > +     PGO_PROFILE_main.o := n
> > +
> > +and
> > +
> > +  .. code-block:: make
> > +
> > +     PGO_PROFILE := n
> > +
> > +Only files which are linked to the main kernel image or are compiled as kernel
> > +modules are supported by this mechanism.
> > +
> > +
> > +Files
> > +=====
> > +
> > +The PGO kernel support creates the following files in debugfs:
> > +
> > +``/sys/kernel/debug/pgo``
> > +       Parent directory for all PGO-related files.
> > +
> > +``/sys/kernel/debug/pgo/reset``
> > +       Global reset file: resets all coverage data to zero when written to.
> > +
> > +``/sys/kernel/debug/profraw``
> > +       The raw PGO data that must be processed with ``llvm_profdata``.
> > +
> > +
> > +Workflow
> > +========
> > +
> > +The PGO kernel can be run on the host or test machines. The data though should
> > +be analyzed with Clang's tools from the same Clang version as the kernel was
> > +compiled. Clang's tolerant of version skew, but it's easier to use the same
> > +Clang version.
> > +
> > +The profiling data is useful for optimizing the kernel, analyzing coverage,
> > +etc. Clang offers tools to perform these tasks.
> > +
> > +Here is an example workflow for profiling an instrumented kernel with PGO and
> > +using the result to optimize the kernel:
> > +
> > +1) Install the kernel on the TEST machine.
> > +
> > +2) Reset the data counters right before running the load tests
> > +
> > +   .. code-block:: sh
> > +
> > +      echo 1 > /sys/kernel/debug/pgo/reset
> > +
> > +3) Run the load tests.
> > +
> > +4) Collect the raw profile data
> > +
> > +   .. code-block:: sh
> > +
> > +      cp -a /sys/kernel/debug/pgo/profraw /tmp/vmlinux.profraw
> > +
> > +5) (Optional) Download the raw profile data to the HOST machine.
> > +
> > +6) Process the raw profile data
> > +
> > +   .. code-block:: sh
> > +
> > +      llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> > +
> > +   Note that multiple raw profile data files can be merged during this step.
> > +
> > +7) Rebuild the kernel using the profile data (PGO disabled)
> > +
> > +   .. code-block:: sh
> > +
> > +      make ... KCLAGS=-fprofile-use=vmlinux.profdata
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 6390491b07e51..7a98bdaab9861 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -13955,6 +13955,15 @@ S:     Maintained
> >  F:     include/linux/personality.h
> >  F:     include/uapi/linux/personality.h
> >
> > +PGO BASED KERNEL PROFILING
> > +M:     Sami Tolvanen <samitolvanen@google.com>
> > +M:     Bill Wendling <wcw@google.com>
> > +R:     Nathan Chancellor <natechancellor@gmail.com>
> > +R:     Nick Desaulniers <ndesaulniers@google.com>
> > +S:     Supported
> > +F:     Documentation/dev-tools/pgo.rst
> > +F:     kernel/pgo
> > +
> >  PHOENIX RC FLIGHT CONTROLLER ADAPTER
> >  M:     Marcus Folkesson <marcus.folkesson@gmail.com>
> >  L:     linux-input@vger.kernel.org
> > diff --git a/Makefile b/Makefile
> > index 8b2c3f88ee5ea..4f42957c78134 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -659,6 +659,9 @@ endif # KBUILD_EXTMOD
> >  # Defaults to vmlinux, but the arch makefile usually adds further targets
> >  all: vmlinux
> >
> > +CFLAGS_PGO_CLANG := -fprofile-generate
> > +export CFLAGS_PGO_CLANG
> > +
> >  CFLAGS_GCOV    := -fprofile-arcs -ftest-coverage \
> >         $(call cc-option,-fno-tree-loop-im) \
> >         $(call cc-disable-warning,maybe-uninitialized,)
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index 78c6f05b10f91..a7a6ab7d204dc 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -1106,6 +1106,7 @@ config ARCH_SUPPORTS_DEBUG_PAGEALLOC
> >         bool
> >
> >  source "kernel/gcov/Kconfig"
> > +source "kernel/pgo/Kconfig"
> >
> >  source "scripts/gcc-plugins/Kconfig"
> >
> > diff --git a/arch/arm/boot/bootp/Makefile b/arch/arm/boot/bootp/Makefile
> > index 981a8d03f064c..523bd58df0a4b 100644
> > --- a/arch/arm/boot/bootp/Makefile
> > +++ b/arch/arm/boot/bootp/Makefile
> > @@ -7,6 +7,7 @@
> >  #
> >
> >  GCOV_PROFILE   := n
> > +PGO_PROFILE    := n
> >
> >  LDFLAGS_bootp  := --no-undefined -X \
> >                  --defsym initrd_phys=$(INITRD_PHYS) \
> > diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
> > index fb521efcc6c20..5fd0fd85fc0e5 100644
> > --- a/arch/arm/boot/compressed/Makefile
> > +++ b/arch/arm/boot/compressed/Makefile
> > @@ -24,6 +24,7 @@ OBJS          += hyp-stub.o
> >  endif
> >
> >  GCOV_PROFILE           := n
> > +PGO_PROFILE            := n
> >  KASAN_SANITIZE         := n
> >
> >  # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
> > diff --git a/arch/arm/vdso/Makefile b/arch/arm/vdso/Makefile
> > index b558bee0e1f6b..11f6ce4b48b56 100644
> > --- a/arch/arm/vdso/Makefile
> > +++ b/arch/arm/vdso/Makefile
> > @@ -36,8 +36,9 @@ else
> >  CFLAGS_vgettimeofday.o = -O2 -include $(c-gettimeofday-y)
> >  endif
> >
> > -# Disable gcov profiling for VDSO code
> > +# Disable gcov and PGO profiling for VDSO code
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> >  # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
> >  KCOV_INSTRUMENT := n
> > diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
> > index cd9c3fa25902f..d48fc0df07020 100644
> > --- a/arch/arm64/kernel/vdso/Makefile
> > +++ b/arch/arm64/kernel/vdso/Makefile
> > @@ -41,8 +41,9 @@ ifneq ($(c-gettimeofday-y),)
> >    CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)
> >  endif
> >
> > -# Disable gcov profiling for VDSO code
> > +# Disable gcov and PGO profiling for VDSO code
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> >  obj-y += vdso.o
> >  targets += vdso.lds
> > diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
> > index 1f1e351c5fe2b..ad128ecdbfbdf 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/Makefile
> > +++ b/arch/arm64/kvm/hyp/nvhe/Makefile
> > @@ -60,6 +60,7 @@ KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS), $(KBUILD_CFLAG
> >  # compiler instrumentation that inserts callbacks or checks into the code may
> >  # cause crashes. Just disable it.
> >  GCOV_PROFILE   := n
> > +PGO_PROFILE    := n
> >  KASAN_SANITIZE := n
> >  UBSAN_SANITIZE := n
> >  KCOV_INSTRUMENT        := n
> > diff --git a/arch/mips/boot/compressed/Makefile b/arch/mips/boot/compressed/Makefile
> > index 47cd9dc7454af..0855ea12f2c7f 100644
> > --- a/arch/mips/boot/compressed/Makefile
> > +++ b/arch/mips/boot/compressed/Makefile
> > @@ -37,6 +37,7 @@ KBUILD_AFLAGS := $(KBUILD_AFLAGS) -D__ASSEMBLY__ \
> >  # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
> >  KCOV_INSTRUMENT                := n
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> >  # decompressor objects (linked with vmlinuz)
> >  vmlinuzobjs-y := $(obj)/head.o $(obj)/decompress.o $(obj)/string.o
> > diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
> > index 5810cc12bc1d9..d7eb64de35eae 100644
> > --- a/arch/mips/vdso/Makefile
> > +++ b/arch/mips/vdso/Makefile
> > @@ -66,6 +66,7 @@ ldflags-y := -Bsymbolic --no-undefined -soname=linux-vdso.so.1 \
> >  CFLAGS_REMOVE_vdso.o = -pg
> >
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE := n
> >  KCOV_INSTRUMENT := n
> >
> > diff --git a/arch/nds32/kernel/vdso/Makefile b/arch/nds32/kernel/vdso/Makefile
> > index 55df25ef00578..f2b53ee2124b7 100644
> > --- a/arch/nds32/kernel/vdso/Makefile
> > +++ b/arch/nds32/kernel/vdso/Makefile
> > @@ -15,9 +15,9 @@ obj-vdso := $(addprefix $(obj)/, $(obj-vdso))
> >  ccflags-y := -shared -fno-common -fno-builtin -nostdlib -fPIC -Wl,-shared -g \
> >         -Wl,-soname=linux-vdso.so.1 -Wl,--hash-style=sysv
> >
> > -# Disable gcov profiling for VDSO code
> > +# Disable gcov and PGO profiling for VDSO code
> >  GCOV_PROFILE := n
> > -
> > +PGO_PROFILE := n
> >
> >  obj-y += vdso.o
> >  targets += vdso.lds
> > diff --git a/arch/parisc/boot/compressed/Makefile b/arch/parisc/boot/compressed/Makefile
> > index dff4536875305..5cf93a67f7da7 100644
> > --- a/arch/parisc/boot/compressed/Makefile
> > +++ b/arch/parisc/boot/compressed/Makefile
> > @@ -7,6 +7,7 @@
> >
> >  KCOV_INSTRUMENT := n
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE := n
> >
> >  targets := vmlinux.lds vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2
> > diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> > index fe2ef598e2ead..c642c046660d7 100644
> > --- a/arch/powerpc/kernel/Makefile
> > +++ b/arch/powerpc/kernel/Makefile
> > @@ -153,17 +153,21 @@ endif
> >  obj-$(CONFIG_PPC_SECURE_BOOT)  += secure_boot.o ima_arch.o secvar-ops.o
> >  obj-$(CONFIG_PPC_SECVAR_SYSFS) += secvar-sysfs.o
> >
> > -# Disable GCOV, KCOV & sanitizers in odd or sensitive code
> > +# Disable GCOV, PGO, KCOV & sanitizers in odd or sensitive code
> >  GCOV_PROFILE_prom_init.o := n
> > +PGO_PROFILE_prom_init.o := n
> >  KCOV_INSTRUMENT_prom_init.o := n
> >  UBSAN_SANITIZE_prom_init.o := n
> >  GCOV_PROFILE_kprobes.o := n
> > +PGO_PROFILE_kprobes.o := n
> >  KCOV_INSTRUMENT_kprobes.o := n
> >  UBSAN_SANITIZE_kprobes.o := n
> >  GCOV_PROFILE_kprobes-ftrace.o := n
> > +PGO_PROFILE_kprobes-ftrace.o := n
> >  KCOV_INSTRUMENT_kprobes-ftrace.o := n
> >  UBSAN_SANITIZE_kprobes-ftrace.o := n
> >  GCOV_PROFILE_syscall_64.o := n
> > +PGO_PROFILE_syscall_64.o := n
> >  KCOV_INSTRUMENT_syscall_64.o := n
> >  UBSAN_SANITIZE_syscall_64.o := n
> >  UBSAN_SANITIZE_vdso.o := n
> > diff --git a/arch/powerpc/kernel/trace/Makefile b/arch/powerpc/kernel/trace/Makefile
> > index 858503775c583..7d72ae7d4f8c6 100644
> > --- a/arch/powerpc/kernel/trace/Makefile
> > +++ b/arch/powerpc/kernel/trace/Makefile
> > @@ -23,7 +23,8 @@ obj-$(CONFIG_TRACING)                 += trace_clock.o
> >  obj-$(CONFIG_PPC64)                    += $(obj64-y)
> >  obj-$(CONFIG_PPC32)                    += $(obj32-y)
> >
> > -# Disable GCOV, KCOV & sanitizers in odd or sensitive code
> > +# Disable GCOV, PGO, KCOV & sanitizers in odd or sensitive code
> >  GCOV_PROFILE_ftrace.o := n
> > +PGO_PROFILE_ftrace.o := n
> >  KCOV_INSTRUMENT_ftrace.o := n
> >  UBSAN_SANITIZE_ftrace.o := n
> > diff --git a/arch/powerpc/kernel/vdso32/Makefile b/arch/powerpc/kernel/vdso32/Makefile
> > index 9cb6f524854b9..655e159975a04 100644
> > --- a/arch/powerpc/kernel/vdso32/Makefile
> > +++ b/arch/powerpc/kernel/vdso32/Makefile
> > @@ -34,6 +34,7 @@ targets := $(obj-vdso32) vdso32.so.dbg
> >  obj-vdso32 := $(addprefix $(obj)/, $(obj-vdso32))
> >
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  KCOV_INSTRUMENT := n
> >  UBSAN_SANITIZE := n
> >  KASAN_SANITIZE := n
> > diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile
> > index bf363ff371521..12c286f5afc16 100644
> > --- a/arch/powerpc/kernel/vdso64/Makefile
> > +++ b/arch/powerpc/kernel/vdso64/Makefile
> > @@ -21,6 +21,7 @@ targets := $(obj-vdso64) vdso64.so.dbg
> >  obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64))
> >
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  KCOV_INSTRUMENT := n
> >  UBSAN_SANITIZE := n
> >  KASAN_SANITIZE := n
> > diff --git a/arch/powerpc/kexec/Makefile b/arch/powerpc/kexec/Makefile
> > index 4aff6846c7726..1c7f65e3cb969 100644
> > --- a/arch/powerpc/kexec/Makefile
> > +++ b/arch/powerpc/kexec/Makefile
> > @@ -16,7 +16,8 @@ endif
> >  endif
> >
> >
> > -# Disable GCOV, KCOV & sanitizers in odd or sensitive code
> > +# Disable GCOV, PGO, KCOV & sanitizers in odd or sensitive code
> >  GCOV_PROFILE_core_$(BITS).o := n
> > +PGO_PROFILE_core_$(BITS).o := n
> >  KCOV_INSTRUMENT_core_$(BITS).o := n
> >  UBSAN_SANITIZE_core_$(BITS).o := n
> > diff --git a/arch/powerpc/xmon/Makefile b/arch/powerpc/xmon/Makefile
> > index eb25d7554ffd1..7aff80d18b44b 100644
> > --- a/arch/powerpc/xmon/Makefile
> > +++ b/arch/powerpc/xmon/Makefile
> > @@ -2,6 +2,7 @@
> >  # Makefile for xmon
> >
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  KCOV_INSTRUMENT := n
> >  UBSAN_SANITIZE := n
> >  KASAN_SANITIZE := n
> > diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
> > index 0cfd6da784f84..882340dc3c647 100644
> > --- a/arch/riscv/kernel/vdso/Makefile
> > +++ b/arch/riscv/kernel/vdso/Makefile
> > @@ -32,8 +32,9 @@ CPPFLAGS_vdso.lds += -P -C -U$(ARCH)
> >  # Disable -pg to prevent insert call site
> >  CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os
> >
> > -# Disable gcov profiling for VDSO code
> > +# Disable gcov and PGO profiling for VDSO code
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  KCOV_INSTRUMENT := n
> >
> >  # Force dependency
> > diff --git a/arch/s390/boot/Makefile b/arch/s390/boot/Makefile
> > index 41a64b8dce252..bee4a32040e79 100644
> > --- a/arch/s390/boot/Makefile
> > +++ b/arch/s390/boot/Makefile
> > @@ -5,6 +5,7 @@
> >
> >  KCOV_INSTRUMENT := n
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE := n
> >  KASAN_SANITIZE := n
> >
> > diff --git a/arch/s390/boot/compressed/Makefile b/arch/s390/boot/compressed/Makefile
> > index de18dab518bb6..c3ab883e8425a 100644
> > --- a/arch/s390/boot/compressed/Makefile
> > +++ b/arch/s390/boot/compressed/Makefile
> > @@ -7,6 +7,7 @@
> >
> >  KCOV_INSTRUMENT := n
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE := n
> >  KASAN_SANITIZE := n
> >
> > diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile
> > index dd73b7f074237..bd857aacad794 100644
> > --- a/arch/s390/kernel/Makefile
> > +++ b/arch/s390/kernel/Makefile
> > @@ -14,6 +14,7 @@ CFLAGS_REMOVE_early.o         = $(CC_FLAGS_FTRACE)
> >  endif
> >
> >  GCOV_PROFILE_early.o           := n
> > +PGO_PROFILE_early.o            := n
> >  KCOV_INSTRUMENT_early.o                := n
> >  UBSAN_SANITIZE_early.o         := n
> >  KASAN_SANITIZE_ipl.o           := n
> > diff --git a/arch/s390/kernel/vdso64/Makefile b/arch/s390/kernel/vdso64/Makefile
> > index a6e0fb6b91d6c..d7c43b7c1db96 100644
> > --- a/arch/s390/kernel/vdso64/Makefile
> > +++ b/arch/s390/kernel/vdso64/Makefile
> > @@ -35,8 +35,9 @@ obj-y += vdso64_wrapper.o
> >  targets += vdso64.lds
> >  CPPFLAGS_vdso64.lds += -P -C -U$(ARCH)
> >
> > -# Disable gcov profiling, ubsan and kasan for VDSO code
> > +# Disable gcov and PGO profiling, ubsan and kasan for VDSO code
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE := n
> >  KASAN_SANITIZE := n
> >
> > diff --git a/arch/s390/purgatory/Makefile b/arch/s390/purgatory/Makefile
> > index c57f8c40e9926..9aef584e98466 100644
> > --- a/arch/s390/purgatory/Makefile
> > +++ b/arch/s390/purgatory/Makefile
> > @@ -17,6 +17,7 @@ $(obj)/mem.o: $(srctree)/arch/s390/lib/mem.S FORCE
> >
> >  KCOV_INSTRUMENT := n
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE := n
> >  KASAN_SANITIZE := n
> >
> > diff --git a/arch/sh/boot/compressed/Makefile b/arch/sh/boot/compressed/Makefile
> > index 589d2d8a573db..ae19aeeb3964c 100644
> > --- a/arch/sh/boot/compressed/Makefile
> > +++ b/arch/sh/boot/compressed/Makefile
> > @@ -13,6 +13,7 @@ targets               := vmlinux vmlinux.bin vmlinux.bin.gz \
> >  OBJECTS = $(obj)/head_32.o $(obj)/misc.o $(obj)/cache.o
> >
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> >  #
> >  # IMAGE_OFFSET is the load offset of the compression loader
> > diff --git a/arch/sh/mm/Makefile b/arch/sh/mm/Makefile
> > index f69ddc70b1465..ea2782c631f43 100644
> > --- a/arch/sh/mm/Makefile
> > +++ b/arch/sh/mm/Makefile
> > @@ -43,3 +43,4 @@ obj-$(CONFIG_UNCACHED_MAPPING)        += uncached.o
> >  obj-$(CONFIG_HAVE_SRAM_POOL)   += sram.o
> >
> >  GCOV_PROFILE_pmb.o := n
> > +PGO_PROFILE_pmb.o := n
> > diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile
> > index c5e1545bc5cf9..ab5f3783fe199 100644
> > --- a/arch/sparc/vdso/Makefile
> > +++ b/arch/sparc/vdso/Makefile
> > @@ -115,6 +115,7 @@ quiet_cmd_vdso = VDSO    $@
> >
> >  VDSO_LDFLAGS = -shared --hash-style=both --build-id=sha1 -Bsymbolic
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> >  #
> >  # Install the unstripped copies of vdso*.so.  If our toolchain supports
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index 7b6dd10b162ac..a751b4f8f6645 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -95,6 +95,7 @@ config X86
> >         select ARCH_SUPPORTS_DEBUG_PAGEALLOC
> >         select ARCH_SUPPORTS_NUMA_BALANCING     if X86_64
> >         select ARCH_SUPPORTS_KMAP_LOCAL_FORCE_MAP       if NR_CPUS <= 4096
> > +       select ARCH_SUPPORTS_PGO_CLANG          if X86_64
> >         select ARCH_USE_BUILTIN_BSWAP
> >         select ARCH_USE_QUEUED_RWLOCKS
> >         select ARCH_USE_QUEUED_SPINLOCKS
> > diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
> > index fe605205b4ce2..383853e32f673 100644
> > --- a/arch/x86/boot/Makefile
> > +++ b/arch/x86/boot/Makefile
> > @@ -71,6 +71,7 @@ KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
> >  KBUILD_CFLAGS  += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
> >  KBUILD_CFLAGS  += -fno-asynchronous-unwind-tables
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE := n
> >
> >  $(obj)/bzImage: asflags-y  := $(SVGA_MODE)
> > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> > index e0bc3988c3faa..ed12ab65f6065 100644
> > --- a/arch/x86/boot/compressed/Makefile
> > +++ b/arch/x86/boot/compressed/Makefile
> > @@ -54,6 +54,7 @@ CFLAGS_sev-es.o += -I$(objtree)/arch/x86/lib/
> >
> >  KBUILD_AFLAGS  := $(KBUILD_CFLAGS) -D__ASSEMBLY__
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE :=n
> >
> >  KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
> > diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> > index 02e3e42f380bd..26e2b3af0145c 100644
> > --- a/arch/x86/entry/vdso/Makefile
> > +++ b/arch/x86/entry/vdso/Makefile
> > @@ -179,6 +179,7 @@ quiet_cmd_vdso = VDSO    $@
> >  VDSO_LDFLAGS = -shared --hash-style=both --build-id=sha1 \
> >         $(call ld-option, --eh-frame-hdr) -Bsymbolic
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> >  quiet_cmd_vdso_and_check = VDSO    $@
> >        cmd_vdso_and_check = $(cmd_vdso); $(cmd_vdso_check)
> > diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> > index efd9e9ea17f25..f6cab2316c46a 100644
> > --- a/arch/x86/kernel/vmlinux.lds.S
> > +++ b/arch/x86/kernel/vmlinux.lds.S
> > @@ -184,6 +184,8 @@ SECTIONS
> >
> >         BUG_TABLE
> >
> > +       PGO_CLANG_DATA
> > +
> >         ORC_UNWIND_TABLE
> >
> >         . = ALIGN(PAGE_SIZE);
> > diff --git a/arch/x86/platform/efi/Makefile b/arch/x86/platform/efi/Makefile
> > index 84b09c230cbd5..5f22b31446ad4 100644
> > --- a/arch/x86/platform/efi/Makefile
> > +++ b/arch/x86/platform/efi/Makefile
> > @@ -2,6 +2,7 @@
> >  OBJECT_FILES_NON_STANDARD_efi_thunk_$(BITS).o := y
> >  KASAN_SANITIZE := n
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> >  obj-$(CONFIG_EFI)              += quirks.o efi.o efi_$(BITS).o efi_stub_$(BITS).o
> >  obj-$(CONFIG_EFI_MIXED)                += efi_thunk_$(BITS).o
> > diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> > index 95ea17a9d20cb..36f20e99da0bc 100644
> > --- a/arch/x86/purgatory/Makefile
> > +++ b/arch/x86/purgatory/Makefile
> > @@ -23,6 +23,7 @@ targets += purgatory.ro purgatory.chk
> >
> >  # Sanitizer, etc. runtimes are unavailable and cannot be linked here.
> >  GCOV_PROFILE   := n
> > +PGO_PROFILE    := n
> >  KASAN_SANITIZE := n
> >  UBSAN_SANITIZE := n
> >  KCSAN_SANITIZE := n
> > diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile
> > index 83f1b6a56449f..21797192f958f 100644
> > --- a/arch/x86/realmode/rm/Makefile
> > +++ b/arch/x86/realmode/rm/Makefile
> > @@ -76,4 +76,5 @@ KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP -D_WAKEUP \
> >  KBUILD_AFLAGS  := $(KBUILD_CFLAGS) -D__ASSEMBLY__
> >  KBUILD_CFLAGS  += -fno-asynchronous-unwind-tables
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE := n
> > diff --git a/arch/x86/um/vdso/Makefile b/arch/x86/um/vdso/Makefile
> > index 5943387e3f357..54f5768f58530 100644
> > --- a/arch/x86/um/vdso/Makefile
> > +++ b/arch/x86/um/vdso/Makefile
> > @@ -64,6 +64,7 @@ quiet_cmd_vdso = VDSO    $@
> >
> >  VDSO_LDFLAGS = -fPIC -shared -Wl,--hash-style=sysv
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> >  #
> >  # Install the unstripped copy of vdso*.so listed in $(vdso-install-y).
> > diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> > index 8a94388e38b33..2d81623b33f29 100644
> > --- a/drivers/firmware/efi/libstub/Makefile
> > +++ b/drivers/firmware/efi/libstub/Makefile
> > @@ -40,6 +40,7 @@ KBUILD_CFLAGS                 := $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
> >  KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))
> >
> >  GCOV_PROFILE                   := n
> > +PGO_PROFILE                    := n
> >  # Sanitizer runtimes are unavailable and cannot be linked here.
> >  KASAN_SANITIZE                 := n
> >  KCSAN_SANITIZE                 := n
> > diff --git a/drivers/s390/char/Makefile b/drivers/s390/char/Makefile
> > index c6fdb81a068a6..bf6c5db5da1fc 100644
> > --- a/drivers/s390/char/Makefile
> > +++ b/drivers/s390/char/Makefile
> > @@ -9,6 +9,7 @@ CFLAGS_REMOVE_sclp_early_core.o = $(CC_FLAGS_FTRACE)
> >  endif
> >
> >  GCOV_PROFILE_sclp_early_core.o         := n
> > +PGO_PROFILE_sclp_early_core.o          := n
> >  KCOV_INSTRUMENT_sclp_early_core.o      := n
> >  UBSAN_SANITIZE_sclp_early_core.o       := n
> >  KASAN_SANITIZE_sclp_early_core.o       := n
> > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> > index b2b3d81b1535a..3a591bb18c5fb 100644
> > --- a/include/asm-generic/vmlinux.lds.h
> > +++ b/include/asm-generic/vmlinux.lds.h
> > @@ -316,6 +316,49 @@
> >  #define THERMAL_TABLE(name)
> >  #endif
> >
> > +#ifdef CONFIG_PGO_CLANG
> > +#define PGO_CLANG_DATA                                                 \
> > +       __llvm_prf_data : AT(ADDR(__llvm_prf_data) - LOAD_OFFSET) {     \
> > +               . = ALIGN(8);                                           \
> > +               __llvm_prf_start = .;                                   \
> > +               __llvm_prf_data_start = .;                              \
> > +               KEEP(*(__llvm_prf_data))                                \
> > +               . = ALIGN(8);                                           \
> > +               __llvm_prf_data_end = .;                                \
> > +       }                                                               \
> > +       __llvm_prf_cnts : AT(ADDR(__llvm_prf_cnts) - LOAD_OFFSET) {     \
> > +               . = ALIGN(8);                                           \
> > +               __llvm_prf_cnts_start = .;                              \
> > +               KEEP(*(__llvm_prf_cnts))                                \
> > +               . = ALIGN(8);                                           \
> > +               __llvm_prf_cnts_end = .;                                \
> > +       }                                                               \
> > +       __llvm_prf_names : AT(ADDR(__llvm_prf_names) - LOAD_OFFSET) {   \
> > +               . = ALIGN(8);                                           \
> > +               __llvm_prf_names_start = .;                             \
> > +               KEEP(*(__llvm_prf_names))                               \
> > +               . = ALIGN(8);                                           \
> > +               __llvm_prf_names_end = .;                               \
> > +               . = ALIGN(8);                                           \
> > +       }                                                               \
> > +       __llvm_prf_vals : AT(ADDR(__llvm_prf_vals) - LOAD_OFFSET) {     \
> > +               __llvm_prf_vals_start = .;                              \
> > +               KEEP(*(__llvm_prf_vals))                                \
> > +               . = ALIGN(8);                                           \
> > +               __llvm_prf_vals_end = .;                                \
> > +               . = ALIGN(8);                                           \
> > +       }                                                               \
> > +       __llvm_prf_vnds : AT(ADDR(__llvm_prf_vnds) - LOAD_OFFSET) {     \
> > +               __llvm_prf_vnds_start = .;                              \
> > +               KEEP(*(__llvm_prf_vnds))                                \
> > +               . = ALIGN(8);                                           \
> > +               __llvm_prf_vnds_end = .;                                \
> > +               __llvm_prf_end = .;                                     \
> > +       }
> > +#else
> > +#define PGO_CLANG_DATA
> > +#endif
> > +
> >  #define KERNEL_DTB()                                                   \
> >         STRUCT_ALIGN();                                                 \
> >         __dtb_start = .;                                                \
> > @@ -1125,6 +1168,7 @@
> >                 CONSTRUCTORS                                            \
> >         }                                                               \
> >         BUG_TABLE                                                       \
> > +       PGO_CLANG_DATA
> >
> >  #define INIT_TEXT_SECTION(inittext_align)                              \
> >         . = ALIGN(inittext_align);                                      \
> > diff --git a/kernel/Makefile b/kernel/Makefile
> > index aa7368c7eabf3..0b34ca228ba46 100644
> > --- a/kernel/Makefile
> > +++ b/kernel/Makefile
> > @@ -111,6 +111,7 @@ obj-$(CONFIG_BPF) += bpf/
> >  obj-$(CONFIG_KCSAN) += kcsan/
> >  obj-$(CONFIG_SHADOW_CALL_STACK) += scs.o
> >  obj-$(CONFIG_HAVE_STATIC_CALL_INLINE) += static_call.o
> > +obj-$(CONFIG_PGO_CLANG) += pgo/
> >
> >  obj-$(CONFIG_PERF_EVENTS) += events/
> >
> > diff --git a/kernel/pgo/Kconfig b/kernel/pgo/Kconfig
> > new file mode 100644
> > index 0000000000000..318d36bb3d106
> > --- /dev/null
> > +++ b/kernel/pgo/Kconfig
> > @@ -0,0 +1,34 @@
> > +# SPDX-License-Identifier: GPL-2.0-only
> > +menu "Profile Guided Optimization (PGO) (EXPERIMENTAL)"
> > +
> > +config ARCH_SUPPORTS_PGO_CLANG
> > +       bool
> > +
> > +config PGO_CLANG
> > +       bool "Enable clang's PGO-based kernel profiling"
> > +       depends on DEBUG_FS
> > +       depends on ARCH_SUPPORTS_PGO_CLANG
> > +       help
> > +         This option enables clang's PGO (Profile Guided Optimization) based
> > +         code profiling to better optimize the kernel.
> > +
> > +         If unsure, say N.
> > +
> > +         Run a representative workload for your application on a kernel
> > +         compiled with this option and download the raw profile file from
> > +         /sys/kernel/debug/pgo/profraw. This file needs to be processed with
> > +         llvm-profdata. It may be merged with other collected raw profiles.
> > +
> > +         Copy the resulting profile file into vmlinux.profdata, and enable
> > +         KCFLAGS=-fprofile-use=vmlinux.profdata to produce an optimized
> > +         kernel.
> > +
> > +         Note that a kernel compiled with profiling flags will be
> > +         significatnly larger and run slower. Also be sure to exclude files
> > +         from profiling which are not linked to the kernel image to prevent
> > +         linker errors.
> > +
> > +         Note that the debugfs filesystem has to be mounted to access
> > +         profiling data.
> > +
> > +endmenu
> > diff --git a/kernel/pgo/Makefile b/kernel/pgo/Makefile
> > new file mode 100644
> > index 0000000000000..41e27cefd9a47
> > --- /dev/null
> > +++ b/kernel/pgo/Makefile
> > @@ -0,0 +1,5 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +GCOV_PROFILE   := n
> > +PGO_PROFILE    := n
> > +
> > +obj-y  += fs.o instrument.o
> > diff --git a/kernel/pgo/fs.c b/kernel/pgo/fs.c
> > new file mode 100644
> > index 0000000000000..790a8df037bfc
> > --- /dev/null
> > +++ b/kernel/pgo/fs.c
> > @@ -0,0 +1,382 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) 2019 Google, Inc.
> > + *
> > + * Author:
> > + *     Sami Tolvanen <samitolvanen@google.com>
> > + *
> > + * This software is licensed under the terms of the GNU General Public
> > + * License version 2, as published by the Free Software Foundation, and
> > + * may be copied, distributed, and modified under those terms.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + *
> > + */
> > +
> > +#define pr_fmt(fmt)    "pgo: " fmt
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/debugfs.h>
> > +#include <linux/fs.h>
> > +#include <linux/module.h>
> > +#include <linux/slab.h>
> > +#include <linux/vmalloc.h>
> > +#include "pgo.h"
> > +
> > +static struct dentry *directory;
> > +
> > +struct prf_private_data {
> > +       void *buffer;
> > +       unsigned long size;
> > +};
> > +
> > +/*
> > + * Raw profile data format:
> > + *
> > + *     - llvm_prf_header
> > + *     - __llvm_prf_data
> > + *     - __llvm_prf_cnts
> > + *     - __llvm_prf_names
> > + *     - zero padding to 8 bytes
> > + *     - for each llvm_prf_data in __llvm_prf_data:
> > + *             - llvm_prf_value_data
> > + *                     - llvm_prf_value_record + site count array
> > + *                             - llvm_prf_value_node_data
> > + *                             ...
> > + *                     ...
> > + *             ...
> > + */
> > +
> > +static void prf_fill_header(void **buffer)
> > +{
> > +       struct llvm_prf_header *header = *(struct llvm_prf_header **)buffer;
> > +
> > +       header->magic = LLVM_PRF_MAGIC;
> > +       header->version = LLVM_PRF_VARIANT_MASK_IR | LLVM_PRF_VERSION;
> > +       header->data_size = prf_data_count();
> > +       header->padding_bytes_before_counters = 0;
> > +       header->counters_size = prf_cnts_count();
> > +       header->padding_bytes_after_counters = 0;
> > +       header->names_size = prf_names_count();
> > +       header->counters_delta = (u64)__llvm_prf_cnts_start;
> > +       header->names_delta = (u64)__llvm_prf_names_start;
> > +       header->value_kind_last = LLVM_PRF_IPVK_LAST;
> > +
> > +       *buffer += sizeof(*header);
> > +}
> > +
> > +/*
> > + * Copy the source into the buffer, incrementing the pointer into buffer in the
> > + * process.
> > + */
> > +static void prf_copy_to_buffer(void **buffer, void *src, unsigned long size)
> > +{
> > +       memcpy(*buffer, src, size);
> > +       *buffer += size;
> > +}
> > +
> > +static u32 __prf_get_value_size(struct llvm_prf_data *p, u32 *value_kinds)
> > +{
> > +       struct llvm_prf_value_node **nodes =
> > +               (struct llvm_prf_value_node **)p->values;
> > +       u32 kinds = 0;
> > +       u32 size = 0;
> > +       unsigned int kind;
> > +       unsigned int n;
> > +       unsigned int s = 0;
> > +
> > +       for (kind = 0; kind < ARRAY_SIZE(p->num_value_sites); kind++) {
> > +               unsigned int sites = p->num_value_sites[kind];
> > +
> > +               if (!sites)
> > +                       continue;
> > +
> > +               /* Record + site count array */
> > +               size += prf_get_value_record_size(sites);
> > +               kinds++;
> > +
> > +               if (!nodes)
> > +                       continue;
> > +
> > +               for (n = 0; n < sites; n++) {
> > +                       u32 count = 0;
> > +                       struct llvm_prf_value_node *site = nodes[s + n];
> > +
> > +                       while (site && ++count <= U8_MAX)
> > +                               site = site->next;
> > +
> > +                       size += count *
> > +                               sizeof(struct llvm_prf_value_node_data);
> > +               }
> > +
> > +               s += sites;
> > +       }
> > +
> > +       if (size)
> > +               size += sizeof(struct llvm_prf_value_data);
> > +
> > +       if (value_kinds)
> > +               *value_kinds = kinds;
> > +
> > +       return size;
> > +}
> > +
> > +static u32 prf_get_value_size(void)
> > +{
> > +       u32 size = 0;
> > +       struct llvm_prf_data *p;
> > +
> > +       for (p = __llvm_prf_data_start; p < __llvm_prf_data_end; p++)
> > +               size += __prf_get_value_size(p, NULL);
> > +
> > +       return size;
> > +}
> > +
> > +/* Serialize the profiling's value. */
> > +static void prf_serialize_value(struct llvm_prf_data *p, void **buffer)
> > +{
> > +       struct llvm_prf_value_data header;
> > +       struct llvm_prf_value_node **nodes =
> > +               (struct llvm_prf_value_node **)p->values;
> > +       unsigned int kind;
> > +       unsigned int n;
> > +       unsigned int s = 0;
> > +
> > +       header.total_size = __prf_get_value_size(p, &header.num_value_kinds);
> > +
> > +       if (!header.num_value_kinds)
> > +               /* Nothing to write. */
> > +               return;
> > +
> > +       prf_copy_to_buffer(buffer, &header, sizeof(header));
> > +
> > +       for (kind = 0; kind < ARRAY_SIZE(p->num_value_sites); kind++) {
> > +               struct llvm_prf_value_record *record;
> > +               u8 *counts;
> > +               unsigned int sites = p->num_value_sites[kind];
> > +
> > +               if (!sites)
> > +                       continue;
> > +
> > +               /* Profiling value record. */
> > +               record = *(struct llvm_prf_value_record **)buffer;
> > +               *buffer += prf_get_value_record_header_size();
> > +
> > +               record->kind = kind;
> > +               record->num_value_sites = sites;
> > +
> > +               /* Site count array. */
> > +               counts = *(u8 **)buffer;
> > +               *buffer += prf_get_value_record_site_count_size(sites);
> > +
> > +               /*
> > +                * If we don't have nodes, we can skip updating the site count
> > +                * array, because the buffer is zero filled.
> > +                */
> > +               if (!nodes)
> > +                       continue;
> > +
> > +               for (n = 0; n < sites; n++) {
> > +                       u32 count = 0;
> > +                       struct llvm_prf_value_node *site = nodes[s + n];
> > +
> > +                       while (site && ++count <= U8_MAX) {
> > +                               prf_copy_to_buffer(buffer, site,
> > +                                                  sizeof(struct llvm_prf_value_node_data));
> > +                               site = site->next;
> > +                       }
> > +
> > +                       counts[n] = (u8)count;
> > +               }
> > +
> > +               s += sites;
> > +       }
> > +}
> > +
> > +static void prf_serialize_values(void **buffer)
> > +{
> > +       struct llvm_prf_data *p;
> > +
> > +       for (p = __llvm_prf_data_start; p < __llvm_prf_data_end; p++)
> > +               prf_serialize_value(p, buffer);
> > +}
> > +
> > +static inline unsigned long prf_get_padding(unsigned long size)
> > +{
> > +       return 8 - (size % 8);
> > +}
> > +
> > +static unsigned long prf_buffer_size(void)
> > +{
> > +       return sizeof(struct llvm_prf_header) +
> > +                       prf_data_size() +
> > +                       prf_cnts_size() +
> > +                       prf_names_size() +
> > +                       prf_get_padding(prf_names_size()) +
> > +                       prf_get_value_size();
> > +}
> > +
> > +/* Serialize the profling data into a format LLVM's tools can understand. */
> > +static int prf_serialize(struct prf_private_data *p)
> > +{
> > +       int err = 0;
> > +       void *buffer;
> > +
> > +       p->size = prf_buffer_size();
> > +       p->buffer = vzalloc(p->size);
> > +
> > +       if (!p->buffer) {
> > +               err = -ENOMEM;
> > +               goto out;
> > +       }
> > +
> > +       buffer = p->buffer;
> > +
> > +       prf_fill_header(&buffer);
> > +       prf_copy_to_buffer(&buffer, __llvm_prf_data_start,  prf_data_size());
> > +       prf_copy_to_buffer(&buffer, __llvm_prf_cnts_start,  prf_cnts_size());
> > +       prf_copy_to_buffer(&buffer, __llvm_prf_names_start, prf_names_size());
> > +       buffer += prf_get_padding(prf_names_size());
> > +
> > +       prf_serialize_values(&buffer);
> > +
> > +out:
> > +       return err;
> > +}
> > +
> > +/* open() implementation for PGO. Creates a copy of the profiling data set. */
> > +static int prf_open(struct inode *inode, struct file *file)
> > +{
> > +       struct prf_private_data *data;
> > +       unsigned long flags;
> > +       int err;
> > +
> > +       data = kzalloc(sizeof(*data), GFP_KERNEL);
> > +       if (!data) {
> > +               err = -ENOMEM;
> > +               goto out;
> > +       }
> > +
> > +       flags = prf_lock();
> > +
> > +       err = prf_serialize(data);
> > +       if (err) {
> > +               kfree(data);
> > +               goto out_unlock;
> > +       }
> > +
> > +       file->private_data = data;
> > +
> > +out_unlock:
> > +       prf_unlock(flags);
> > +out:
> > +       return err;
> > +}
> > +
> > +/* read() implementation for PGO. */
> > +static ssize_t prf_read(struct file *file, char __user *buf, size_t count,
> > +                       loff_t *ppos)
> > +{
> > +       struct prf_private_data *data = file->private_data;
> > +
> > +       BUG_ON(!data);
> > +
> > +       return simple_read_from_buffer(buf, count, ppos, data->buffer,
> > +                                      data->size);
> > +}
> > +
> > +/* release() implementation for PGO. Release resources allocated by open(). */
> > +static int prf_release(struct inode *inode, struct file *file)
> > +{
> > +       struct prf_private_data *data = file->private_data;
> > +
> > +       if (data) {
> > +               vfree(data->buffer);
> > +               kfree(data);
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> > +static const struct file_operations prf_fops = {
> > +       .owner          = THIS_MODULE,
> > +       .open           = prf_open,
> > +       .read           = prf_read,
> > +       .llseek         = default_llseek,
> > +       .release        = prf_release
> > +};
> > +
> > +/* write() implementation for resetting PGO's profile data. */
> > +static ssize_t reset_write(struct file *file, const char __user *addr,
> > +                          size_t len, loff_t *pos)
> > +{
> > +       struct llvm_prf_data *data;
> > +
> > +       memset(__llvm_prf_cnts_start, 0, prf_cnts_size());
> > +
> > +       for (data = __llvm_prf_data_start; data < __llvm_prf_data_end; ++data) {
> > +               struct llvm_prf_value_node **vnodes;
> > +               u64 current_vsite_count;
> > +               u32 i;
> > +
> > +               if (!data->values)
> > +                       continue;
> > +
> > +               current_vsite_count = 0;
> > +               vnodes = (struct llvm_prf_value_node **)data->values;
> > +
> > +               for (i = LLVM_PRF_IPVK_FIRST; i <= LLVM_PRF_IPVK_LAST; ++i)
> > +                       current_vsite_count += data->num_value_sites[i];
> > +
> > +               for (i = 0; i < current_vsite_count; ++i) {
> > +                       struct llvm_prf_value_node *current_vnode = vnodes[i];
> > +
> > +                       while (current_vnode) {
> > +                               current_vnode->count = 0;
> > +                               current_vnode = current_vnode->next;
> > +                       }
> > +               }
> > +       }
> > +
> > +       return len;
> > +}
> > +
> > +static const struct file_operations prf_reset_fops = {
> > +       .owner          = THIS_MODULE,
> > +       .write          = reset_write,
> > +       .llseek         = noop_llseek,
> > +};
> > +
> > +/* Create debugfs entries. */
> > +static int __init pgo_init(void)
> > +{
> > +       directory = debugfs_create_dir("pgo", NULL);
> > +       if (!directory)
> > +               goto err_remove;
> > +
> > +       if (!debugfs_create_file("profraw", 0600, directory, NULL,
> > +                                &prf_fops))
> > +               goto err_remove;
> > +
> > +       if (!debugfs_create_file("reset", 0200, directory, NULL,
> > +                                &prf_reset_fops))
> > +               goto err_remove;
> > +
> > +       return 0;
> > +
> > +err_remove:
> > +       pr_err("initialization failed\n");
> > +       return -EIO;
> > +}
> > +
> > +/* Remove debufs entries. */
> > +static void __exit pgo_exit(void)
> > +{
> > +       debugfs_remove_recursive(directory);
> > +}
> > +
> > +module_init(pgo_init);
> > +module_exit(pgo_exit);
> > diff --git a/kernel/pgo/instrument.c b/kernel/pgo/instrument.c
> > new file mode 100644
> > index 0000000000000..d96b61a1cf712
> > --- /dev/null
> > +++ b/kernel/pgo/instrument.c
> > @@ -0,0 +1,147 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) 2019 Google, Inc.
> > + *
> > + * Author:
> > + *     Sami Tolvanen <samitolvanen@google.com>
> > + *
> > + * This software is licensed under the terms of the GNU General Public
> > + * License version 2, as published by the Free Software Foundation, and
> > + * may be copied, distributed, and modified under those terms.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + *
> > + */
> > +
> > +#define pr_fmt(fmt)    "pgo: " fmt
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/export.h>
> > +#include <linux/spinlock.h>
> > +#include <linux/types.h>
> > +#include "pgo.h"
> > +
> > +/* Lock guarding value node access and serialization. */
> > +static DEFINE_SPINLOCK(pgo_lock);
> > +static int current_node;
> > +
> > +unsigned long prf_lock(void)
> > +{
> > +       unsigned long flags;
> > +
> > +       spin_lock_irqsave(&pgo_lock, flags);
> > +
> > +       return flags;
> > +}
> > +
> > +void prf_unlock(unsigned long flags)
> > +{
> > +       spin_unlock_irqrestore(&pgo_lock, flags);
> > +}
> > +
> > +/*
> > + * Return a newly allocated profiling value node which contains the tracked
> > + * value by the value profiler.
> > + * Note: caller *must* hold pgo_lock.
> > + */
> > +static struct llvm_prf_value_node *allocate_node(struct llvm_prf_data *p,
> > +                                                u32 index, u64 value)
> > +{
> > +       if (&__llvm_prf_vnds_start[current_node + 1] >= __llvm_prf_vnds_end)
> > +               return NULL; /* Out of nodes */
> > +
> > +       current_node++;
> > +
> > +       /* Make sure the node is entirely within the section */
> > +       if (&__llvm_prf_vnds_start[current_node] >= __llvm_prf_vnds_end ||
> > +           &__llvm_prf_vnds_start[current_node + 1] > __llvm_prf_vnds_end)
> > +               return NULL;
> > +
> > +       return &__llvm_prf_vnds_start[current_node];
> > +}
> > +
> > +/*
> > + * Counts the number of times a target value is seen.
> > + *
> > + * Records the target value for the CounterIndex if not seen before. Otherwise,
> > + * increments the counter associated w/ the target value.
> > + */
> > +void __llvm_profile_instrument_target(u64 target_value, void *data, u32 index)
> > +{
> > +       struct llvm_prf_data *p = (struct llvm_prf_data *)data;
> > +       struct llvm_prf_value_node **counters;
> > +       struct llvm_prf_value_node *curr;
> > +       struct llvm_prf_value_node *min = NULL;
> > +       struct llvm_prf_value_node *prev = NULL;
> > +       u64 min_count = U64_MAX;
> > +       u8 values = 0;
> > +       unsigned long flags;
> > +
> > +       if (!p || !p->values)
> > +               return;
> > +
> > +       counters = (struct llvm_prf_value_node **)p->values;
> > +       curr = counters[index];
> > +
> > +       while (curr) {
> > +               if (target_value == curr->value) {
> > +                       curr->count++;
> > +                       return;
> > +               }
> > +
> > +               if (curr->count < min_count) {
> > +                       min_count = curr->count;
> > +                       min = curr;
> > +               }
> > +
> > +               prev = curr;
> > +               curr = curr->next;
> > +               values++;
> > +       }
> > +
> > +       if (values >= LLVM_PRF_MAX_NUM_VALS_PER_SITE) {
> > +               if (!min->count || !(--min->count)) {
> > +                       curr = min;
> > +                       curr->value = target_value;
> > +                       curr->count++;
> > +               }
> > +               return;
> > +       }
> > +
> > +       /* Lock when updating the value node structure. */
> > +       flags = prf_lock();
> > +
> > +       curr = allocate_node(p, index, target_value);
> > +       if (!curr)
> > +               goto out;
> > +
> > +       curr->value = target_value;
> > +       curr->count++;
> > +
> > +       if (!counters[index])
> > +               counters[index] = curr;
> > +       else if (prev && !prev->next)
> > +               prev->next = curr;
> > +
> > +out:
> > +       prf_unlock(flags);
> > +}
> > +EXPORT_SYMBOL(__llvm_profile_instrument_target);
> > +
> > +/* Counts the number of times a range of targets values are seen. */
> > +void __llvm_profile_instrument_range(u64 target_value, void *data,
> > +                                    u32 index, s64 precise_start,
> > +                                    s64 precise_last, s64 large_value)
> > +{
> > +       if (large_value != S64_MIN && (s64)target_value >= large_value)
> > +               target_value = large_value;
> > +       else if ((s64)target_value < precise_start ||
> > +                (s64)target_value > precise_last)
> > +               target_value = precise_last + 1;
> > +
> > +       __llvm_profile_instrument_target(target_value, data, index);
> > +}
> > +EXPORT_SYMBOL(__llvm_profile_instrument_range);
> > diff --git a/kernel/pgo/pgo.h b/kernel/pgo/pgo.h
> > new file mode 100644
> > index 0000000000000..df0aa278f28bd
> > --- /dev/null
> > +++ b/kernel/pgo/pgo.h
> > @@ -0,0 +1,206 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright (C) 2019 Google, Inc.
> > + *
> > + * Author:
> > + *     Sami Tolvanen <samitolvanen@google.com>
> > + *
> > + * This software is licensed under the terms of the GNU General Public
> > + * License version 2, as published by the Free Software Foundation, and
> > + * may be copied, distributed, and modified under those terms.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + *
> > + */
> > +
> > +#ifndef _PGO_H
> > +#define _PGO_H
> > +
> > +/*
> > + * Note: These internal LLVM definitions must match the compiler version.
> > + * See llvm/include/llvm/ProfileData/InstrProfData.inc in LLVM's source code.
> > + */
> > +
> > +#ifdef CONFIG_64BIT
> > +       #define LLVM_PRF_MAGIC          \
> > +               ((u64)255 << 56 |       \
> > +                (u64)'l' << 48 |       \
> > +                (u64)'p' << 40 |       \
> > +                (u64)'r' << 32 |       \
> > +                (u64)'o' << 24 |       \
> > +                (u64)'f' << 16 |       \
> > +                (u64)'r' << 8  |       \
> > +                (u64)129)
> > +#else
> > +       #define LLVM_PRF_MAGIC          \
> > +               ((u64)255 << 56 |       \
> > +                (u64)'l' << 48 |       \
> > +                (u64)'p' << 40 |       \
> > +                (u64)'r' << 32 |       \
> > +                (u64)'o' << 24 |       \
> > +                (u64)'f' << 16 |       \
> > +                (u64)'R' << 8  |       \
> > +                (u64)129)
> > +#endif
> > +
> > +#define LLVM_PRF_VERSION               5
> > +#define LLVM_PRF_DATA_ALIGN            8
> > +#define LLVM_PRF_IPVK_FIRST            0
> > +#define LLVM_PRF_IPVK_LAST             1
> > +#define LLVM_PRF_MAX_NUM_VALS_PER_SITE 16
> > +
> > +#define LLVM_PRF_VARIANT_MASK_IR       (0x1ull << 56)
> > +#define LLVM_PRF_VARIANT_MASK_CSIR     (0x1ull << 57)
> > +
> > +/**
> > + * struct llvm_prf_header - represents the raw profile header data structure.
> > + * @magic: the magic token for the file format.
> > + * @version: the version of the file format.
> > + * @data_size: the number of entries in the profile data section.
> > + * @padding_bytes_before_counters: the number of padding bytes before the
> > + *   counters.
> > + * @counters_size: the size in bytes of the LLVM profile section containing the
> > + *   counters.
> > + * @padding_bytes_after_counters: the number of padding bytes after the
> > + *   counters.
> > + * @names_size: the size in bytes of the LLVM profile section containing the
> > + *   counters' names.
> > + * @counters_delta: the beginning of the LLMV profile counters section.
> > + * @names_delta: the beginning of the LLMV profile names section.
> > + * @value_kind_last: the last profile value kind.
> > + */
> > +struct llvm_prf_header {
> > +       u64 magic;
> > +       u64 version;
> > +       u64 data_size;
> > +       u64 padding_bytes_before_counters;
> > +       u64 counters_size;
> > +       u64 padding_bytes_after_counters;
> > +       u64 names_size;
> > +       u64 counters_delta;
> > +       u64 names_delta;
> > +       u64 value_kind_last;
> > +};
> > +
> > +/**
> > + * struct llvm_prf_data - represents the per-function control structure.
> > + * @name_ref: the reference to the function's name.
> > + * @func_hash: the hash value of the function.
> > + * @counter_ptr: a pointer to the profile counter.
> > + * @function_ptr: a pointer to the function.
> > + * @values: the profiling values associated with this function.
> > + * @num_counters: the number of counters in the function.
> > + * @num_value_sites: the number of value profile sites.
> > + */
> > +struct llvm_prf_data {
> > +       const u64 name_ref;
> > +       const u64 func_hash;
> > +       const void *counter_ptr;
> > +       const void *function_ptr;
> > +       void *values;
> > +       const u32 num_counters;
> > +       const u16 num_value_sites[LLVM_PRF_IPVK_LAST + 1];
> > +} __aligned(LLVM_PRF_DATA_ALIGN);
> > +
> > +/**
> > + * structure llvm_prf_value_node_data - represents the data part of the struct
> > + *   llvm_prf_value_node data structure.
> > + * @value: the value counters.
> > + * @count: the counters' count.
> > + */
> > +struct llvm_prf_value_node_data {
> > +       u64 value;
> > +       u64 count;
> > +};
> > +
> > +/**
> > + * struct llvm_prf_value_node - represents an internal data structure used by
> > + *   the value profiler.
> > + * @value: the value counters.
> > + * @count: the counters' count.
> > + * @next: the next value node.
> > + */
> > +struct llvm_prf_value_node {
> > +       u64 value;
> > +       u64 count;
> > +       struct llvm_prf_value_node *next;
> > +};
> > +
> > +/**
> > + * struct llvm_prf_value_data - represents the value profiling data in indexed
> > + *   format.
> > + * @total_size: the total size in bytes including this field.
> > + * @num_value_kinds: the number of value profile kinds that has value profile
> > + *   data.
> > + */
> > +struct llvm_prf_value_data {
> > +       u32 total_size;
> > +       u32 num_value_kinds;
> > +};
> > +
> > +/**
> > + * struct llvm_prf_value_record - represents the on-disk layout of the value
> > + *   profile data of a particular kind for one function.
> > + * @kind: the kind of the value profile record.
> > + * @num_value_sites: the number of value profile sites.
> > + * @site_count_array: the first element of the array that stores the number
> > + *   of profiled values for each value site.
> > + */
> > +struct llvm_prf_value_record {
> > +       u32 kind;
> > +       u32 num_value_sites;
> > +       u8 site_count_array[];
> > +};
> > +
> > +#define prf_get_value_record_header_size()             \
> > +       offsetof(struct llvm_prf_value_record, site_count_array)
> > +#define prf_get_value_record_site_count_size(sites)    \
> > +       roundup((sites), 8)
> > +#define prf_get_value_record_size(sites)               \
> > +       (prf_get_value_record_header_size() +           \
> > +        prf_get_value_record_site_count_size((sites)))
> > +
> > +/* Data sections */
> > +extern struct llvm_prf_data __llvm_prf_data_start[];
> > +extern struct llvm_prf_data __llvm_prf_data_end[];
> > +
> > +extern u64 __llvm_prf_cnts_start[];
> > +extern u64 __llvm_prf_cnts_end[];
> > +
> > +extern char __llvm_prf_names_start[];
> > +extern char __llvm_prf_names_end[];
> > +
> > +extern struct llvm_prf_value_node __llvm_prf_vnds_start[];
> > +extern struct llvm_prf_value_node __llvm_prf_vnds_end[];
> > +
> > +/* Locking for vnodes */
> > +extern unsigned long prf_lock(void);
> > +extern void prf_unlock(unsigned long flags);
> > +
> > +#define __DEFINE_PRF_SIZE(s) \
> > +       static inline unsigned long prf_ ## s ## _size(void)            \
> > +       {                                                               \
> > +               unsigned long start =                                   \
> > +                       (unsigned long)__llvm_prf_ ## s ## _start;      \
> > +               unsigned long end =                                     \
> > +                       (unsigned long)__llvm_prf_ ## s ## _end;        \
> > +               return roundup(end - start,                             \
> > +                               sizeof(__llvm_prf_ ## s ## _start[0])); \
> > +       }                                                               \
> > +       static inline unsigned long prf_ ## s ## _count(void)           \
> > +       {                                                               \
> > +               return prf_ ## s ## _size() /                           \
> > +                       sizeof(__llvm_prf_ ## s ## _start[0]);          \
> > +       }
> > +
> > +__DEFINE_PRF_SIZE(data);
> > +__DEFINE_PRF_SIZE(cnts);
> > +__DEFINE_PRF_SIZE(names);
> > +__DEFINE_PRF_SIZE(vnds);
> > +
> > +#undef __DEFINE_PRF_SIZE
> > +
> > +#endif /* _PGO_H */
> > diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> > index 213677a5ed33e..9b218afb5cb87 100644
> > --- a/scripts/Makefile.lib
> > +++ b/scripts/Makefile.lib
> > @@ -143,6 +143,16 @@ _c_flags += $(if $(patsubst n%,, \
> >                 $(CFLAGS_GCOV))
> >  endif
> >
> > +#
> > +# Enable clang's PGO profiling flags for a file or directory depending on
> > +# variables PGO_PROFILE_obj.o and PGO_PROFILE.
> > +#
> > +ifeq ($(CONFIG_PGO_CLANG),y)
> > +_c_flags += $(if $(patsubst n%,, \
> > +               $(PGO_PROFILE_$(basetarget).o)$(PGO_PROFILE)y), \
> > +               $(CFLAGS_PGO_CLANG))
> > +endif
> > +
> >  #
> >  # Enable address sanitizer flags for kernel except some files or directories
> >  # we don't want to check (depends on variables KASAN_SANITIZE_obj.o, KASAN_SANITIZE)
> > --
> > 2.30.0.284.gd98b1dd5eaa7-goog
> >
> > --
> > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
> > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@googlegroups.com.
> > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20210111081821.3041587-1-morbo%40google.com.
Bill Wendling Jan. 11, 2021, 9:17 a.m. UTC | #3
On Mon, Jan 11, 2021 at 12:39 AM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Mon, Jan 11, 2021 at 9:18 AM 'Bill Wendling' via Clang Built Linux
> <clang-built-linux@googlegroups.com> wrote:
> >
> > From: Sami Tolvanen <samitolvanen@google.com>
> >
> > Enable the use of clang's Profile-Guided Optimization[1]. To generate a
> > profile, the kernel is instrumented with PGO counters, a representative
> > workload is run, and the raw profile data is collected from
> > /sys/kernel/debug/pgo/profraw.
> >
> > The raw profile data must be processed by clang's "llvm-profdata" tool before
> > it can be used during recompilation:
> >
> >   $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
> >   $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> >
> > Multiple raw profiles may be merged during this step.
> >
> > The data can be used either by the compiler if LTO isn't enabled:
> >
> >     ... -fprofile-use=vmlinux.profdata ...
> >
> > or by LLD if LTO is enabled:
> >
> >     ... -lto-cs-profile-file=vmlinux.profdata ...
> >
> > This initial submission is restricted to x86, as that's the platform we know
> > works. This restriction can be lifted once other platforms have been verified
> > to work with PGO.
> >
> > Note that this method of profiling the kernel is clang-native and isn't
> > compatible with clang's gcov support in kernel/gcov.
> >
> > [1] https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
> >
>
> Hi Bill and Sami,
>
> I have seen the pull-request in the CBL issue tracker and had some
> questions in mind.
>
> Good you send this.
>
> First of all, I like to fetch any development stuff easily from a Git
> repository.

The version in the pull-request in the CBL issue tracker is roughly
the same as this patch. (There are some changes, but they aren't
functionality changes.)

> Can you offer this, please?
> What is the base for your work?
> I hope this is (fresh released) Linux v5.11-rc3.
>
This patch (and the PR on the CBL issue tracker) are from top-of-tree Linux.

> I myself had some experiences with a PGO + ThinLTO optimized LLVM
> toolchain built with the help of tc-build.
> Here it takes very long to build it.
>
> This means I have some profile-data archived.
> Can I use it?
>
LLVM is more tolerant of "stale" profile data than gcov, so it's
possible that your archived profile data would still work, but I can't
guarantee that it will be better than using new profile data.

> Is an own PGO + ThinLTO optimized LLVM toolchain pre-requirement for
> this or not?
> That is one of my important questions.
>
Do you mean that the LLVM tools (clang, llc, etc.) are compiled with
PGO + ThinLTO?

-bw
Sedat Dilek Jan. 11, 2021, 9:57 a.m. UTC | #4
On Mon, Jan 11, 2021 at 10:17 AM Bill Wendling <morbo@google.com> wrote:
>
> On Mon, Jan 11, 2021 at 12:39 AM Sedat Dilek <sedat.dilek@gmail.com> wrote:
> >
> > On Mon, Jan 11, 2021 at 9:18 AM 'Bill Wendling' via Clang Built Linux
> > <clang-built-linux@googlegroups.com> wrote:
> > >
> > > From: Sami Tolvanen <samitolvanen@google.com>
> > >
> > > Enable the use of clang's Profile-Guided Optimization[1]. To generate a
> > > profile, the kernel is instrumented with PGO counters, a representative
> > > workload is run, and the raw profile data is collected from
> > > /sys/kernel/debug/pgo/profraw.
> > >
> > > The raw profile data must be processed by clang's "llvm-profdata" tool before
> > > it can be used during recompilation:
> > >
> > >   $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
> > >   $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> > >
> > > Multiple raw profiles may be merged during this step.
> > >
> > > The data can be used either by the compiler if LTO isn't enabled:
> > >
> > >     ... -fprofile-use=vmlinux.profdata ...
> > >
> > > or by LLD if LTO is enabled:
> > >
> > >     ... -lto-cs-profile-file=vmlinux.profdata ...
> > >
> > > This initial submission is restricted to x86, as that's the platform we know
> > > works. This restriction can be lifted once other platforms have been verified
> > > to work with PGO.
> > >
> > > Note that this method of profiling the kernel is clang-native and isn't
> > > compatible with clang's gcov support in kernel/gcov.
> > >
> > > [1] https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
> > >
> >
> > Hi Bill and Sami,
> >
> > I have seen the pull-request in the CBL issue tracker and had some
> > questions in mind.
> >
> > Good you send this.
> >
> > First of all, I like to fetch any development stuff easily from a Git
> > repository.
>
> The version in the pull-request in the CBL issue tracker is roughly
> the same as this patch. (There are some changes, but they aren't
> functionality changes.)
>
> > Can you offer this, please?
> > What is the base for your work?
> > I hope this is (fresh released) Linux v5.11-rc3.
> >
> This patch (and the PR on the CBL issue tracker) are from top-of-tree Linux.
>
> > I myself had some experiences with a PGO + ThinLTO optimized LLVM
> > toolchain built with the help of tc-build.
> > Here it takes very long to build it.
> >
> > This means I have some profile-data archived.
> > Can I use it?
> >
> LLVM is more tolerant of "stale" profile data than gcov, so it's
> possible that your archived profile data would still work, but I can't
> guarantee that it will be better than using new profile data.
>
> > Is an own PGO + ThinLTO optimized LLVM toolchain pre-requirement for
> > this or not?
> > That is one of my important questions.
> >
> Do you mean that the LLVM tools (clang, llc, etc.) are compiled with
> PGO + ThinLTO?
>

Yes.

- Sedat -
Nathan Chancellor Jan. 11, 2021, 6:28 p.m. UTC | #5
On Mon, Jan 11, 2021 at 10:57:35AM +0100, Sedat Dilek wrote:
> On Mon, Jan 11, 2021 at 10:17 AM Bill Wendling <morbo@google.com> wrote:
> >
> > On Mon, Jan 11, 2021 at 12:39 AM Sedat Dilek <sedat.dilek@gmail.com> wrote:
> > >
> > > On Mon, Jan 11, 2021 at 9:18 AM 'Bill Wendling' via Clang Built Linux
> > > <clang-built-linux@googlegroups.com> wrote:
> > > >
> > > > From: Sami Tolvanen <samitolvanen@google.com>
> > > >
> > > > Enable the use of clang's Profile-Guided Optimization[1]. To generate a
> > > > profile, the kernel is instrumented with PGO counters, a representative
> > > > workload is run, and the raw profile data is collected from
> > > > /sys/kernel/debug/pgo/profraw.
> > > >
> > > > The raw profile data must be processed by clang's "llvm-profdata" tool before
> > > > it can be used during recompilation:
> > > >
> > > >   $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
> > > >   $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> > > >
> > > > Multiple raw profiles may be merged during this step.
> > > >
> > > > The data can be used either by the compiler if LTO isn't enabled:
> > > >
> > > >     ... -fprofile-use=vmlinux.profdata ...
> > > >
> > > > or by LLD if LTO is enabled:
> > > >
> > > >     ... -lto-cs-profile-file=vmlinux.profdata ...
> > > >
> > > > This initial submission is restricted to x86, as that's the platform we know
> > > > works. This restriction can be lifted once other platforms have been verified
> > > > to work with PGO.
> > > >
> > > > Note that this method of profiling the kernel is clang-native and isn't
> > > > compatible with clang's gcov support in kernel/gcov.
> > > >
> > > > [1] https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
> > > >
> > >
> > > Hi Bill and Sami,
> > >
> > > I have seen the pull-request in the CBL issue tracker and had some
> > > questions in mind.
> > >
> > > Good you send this.
> > >
> > > First of all, I like to fetch any development stuff easily from a Git
> > > repository.
> >
> > The version in the pull-request in the CBL issue tracker is roughly
> > the same as this patch. (There are some changes, but they aren't
> > functionality changes.)
> >
> > > Can you offer this, please?
> > > What is the base for your work?
> > > I hope this is (fresh released) Linux v5.11-rc3.
> > >
> > This patch (and the PR on the CBL issue tracker) are from top-of-tree Linux.
> >
> > > I myself had some experiences with a PGO + ThinLTO optimized LLVM
> > > toolchain built with the help of tc-build.
> > > Here it takes very long to build it.
> > >
> > > This means I have some profile-data archived.
> > > Can I use it?
> > >
> > LLVM is more tolerant of "stale" profile data than gcov, so it's
> > possible that your archived profile data would still work, but I can't
> > guarantee that it will be better than using new profile data.
> >
> > > Is an own PGO + ThinLTO optimized LLVM toolchain pre-requirement for
> > > this or not?
> > > That is one of my important questions.
> > >
> > Do you mean that the LLVM tools (clang, llc, etc.) are compiled with
> > PGO + ThinLTO?
> >
> 
> Yes.
> 
> - Sedat -

No, having an optimized LLVM toolchain is not a requirement of this
patchset. It will make compiling the kernel faster but it does nothing
more than that.

Cheers,
Nathan
Fangrui Song Jan. 11, 2021, 8:12 p.m. UTC | #6
On 2021-01-11, 'Bill Wendling' via Clang Built Linux wrote:
>From: Sami Tolvanen <samitolvanen@google.com>
>
>Enable the use of clang's Profile-Guided Optimization[1]. To generate a
>profile, the kernel is instrumented with PGO counters, a representative
>workload is run, and the raw profile data is collected from
>/sys/kernel/debug/pgo/profraw.
>
>The raw profile data must be processed by clang's "llvm-profdata" tool before
>it can be used during recompilation:
>
>  $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
>  $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
>
>Multiple raw profiles may be merged during this step.
>
>The data can be used either by the compiler if LTO isn't enabled:
>
>    ... -fprofile-use=vmlinux.profdata ...
>
>or by LLD if LTO is enabled:
>
>    ... -lto-cs-profile-file=vmlinux.profdata ...

This LLD option does not exist.
LLD does have some `--lto-*` options but the `-lto-*` form is not supported
(it clashes with -l) https://reviews.llvm.org/D79371

(There is an earlier -fprofile-instr-generate which does
instrumentation in Clang, but the option does not have broad usage.
It is used more for code coverage, not for optimization.
Noticeably, it does not even implement the Kirchhoff's current law
optimization)

-fprofile-use= is used by both regular PGO and context-sensitive PGO (CSPGO).

clang -flto=thin -fprofile-use= passes -plugin-opt=cs-profile-path= to the linker.
For regular PGO, this option is effectively a no-op (confirmed with CSPGO main developer).

So I think the "or by LLD if LTO is enabled:" part should be removed.

>This initial submission is restricted to x86, as that's the platform we know
>works. This restriction can be lifted once other platforms have been verified
>to work with PGO.
>
>Note that this method of profiling the kernel is clang-native and isn't
>compatible with clang's gcov support in kernel/gcov.
>
>[1] https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
>
>Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
>Co-developed-by: Bill Wendling <morbo@google.com>
>Signed-off-by: Bill Wendling <morbo@google.com>
>---
> Documentation/dev-tools/index.rst     |   1 +
> Documentation/dev-tools/pgo.rst       | 127 +++++++++
> MAINTAINERS                           |   9 +
> Makefile                              |   3 +
> arch/Kconfig                          |   1 +
> arch/arm/boot/bootp/Makefile          |   1 +
> arch/arm/boot/compressed/Makefile     |   1 +
> arch/arm/vdso/Makefile                |   3 +-
> arch/arm64/kernel/vdso/Makefile       |   3 +-
> arch/arm64/kvm/hyp/nvhe/Makefile      |   1 +
> arch/mips/boot/compressed/Makefile    |   1 +
> arch/mips/vdso/Makefile               |   1 +
> arch/nds32/kernel/vdso/Makefile       |   4 +-
> arch/parisc/boot/compressed/Makefile  |   1 +
> arch/powerpc/kernel/Makefile          |   6 +-
> arch/powerpc/kernel/trace/Makefile    |   3 +-
> arch/powerpc/kernel/vdso32/Makefile   |   1 +
> arch/powerpc/kernel/vdso64/Makefile   |   1 +
> arch/powerpc/kexec/Makefile           |   3 +-
> arch/powerpc/xmon/Makefile            |   1 +
> arch/riscv/kernel/vdso/Makefile       |   3 +-
> arch/s390/boot/Makefile               |   1 +
> arch/s390/boot/compressed/Makefile    |   1 +
> arch/s390/kernel/Makefile             |   1 +
> arch/s390/kernel/vdso64/Makefile      |   3 +-
> arch/s390/purgatory/Makefile          |   1 +
> arch/sh/boot/compressed/Makefile      |   1 +
> arch/sh/mm/Makefile                   |   1 +
> arch/sparc/vdso/Makefile              |   1 +
> arch/x86/Kconfig                      |   1 +
> arch/x86/boot/Makefile                |   1 +
> arch/x86/boot/compressed/Makefile     |   1 +
> arch/x86/entry/vdso/Makefile          |   1 +
> arch/x86/kernel/vmlinux.lds.S         |   2 +
> arch/x86/platform/efi/Makefile        |   1 +
> arch/x86/purgatory/Makefile           |   1 +
> arch/x86/realmode/rm/Makefile         |   1 +
> arch/x86/um/vdso/Makefile             |   1 +
> drivers/firmware/efi/libstub/Makefile |   1 +
> drivers/s390/char/Makefile            |   1 +
> include/asm-generic/vmlinux.lds.h     |  44 +++
> kernel/Makefile                       |   1 +
> kernel/pgo/Kconfig                    |  34 +++
> kernel/pgo/Makefile                   |   5 +
> kernel/pgo/fs.c                       | 382 ++++++++++++++++++++++++++
> kernel/pgo/instrument.c               | 147 ++++++++++
> kernel/pgo/pgo.h                      | 206 ++++++++++++++
> scripts/Makefile.lib                  |  10 +
> 48 files changed, 1017 insertions(+), 9 deletions(-)
> create mode 100644 Documentation/dev-tools/pgo.rst
> create mode 100644 kernel/pgo/Kconfig
> create mode 100644 kernel/pgo/Makefile
> create mode 100644 kernel/pgo/fs.c
> create mode 100644 kernel/pgo/instrument.c
> create mode 100644 kernel/pgo/pgo.h
>
>diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst
>index f7809c7b1ba9e..8d6418e858062 100644
>--- a/Documentation/dev-tools/index.rst
>+++ b/Documentation/dev-tools/index.rst
>@@ -26,6 +26,7 @@ whole; patches welcome!
>    kgdb
>    kselftest
>    kunit/index
>+   pgo
>
>
> .. only::  subproject and html
>diff --git a/Documentation/dev-tools/pgo.rst b/Documentation/dev-tools/pgo.rst
>new file mode 100644
>index 0000000000000..2ed7f549b20ef
>--- /dev/null
>+++ b/Documentation/dev-tools/pgo.rst
>@@ -0,0 +1,127 @@
>+.. SPDX-License-Identifier: GPL-2.0
>+
>+===============================
>+Using PGO with the Linux kernel
>+===============================
>+
>+Clang's profiling kernel support (PGO_) enables profiling of the Linux kernel
>+when building with Clang. The profiling data is exported via the ``pgo``
>+debugfs directory.
>+
>+.. _PGO: https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
>+
>+
>+Preparation
>+===========
>+
>+Configure the kernel with:
>+
>+.. code-block:: make
>+
>+   CONFIG_DEBUG_FS=y
>+   CONFIG_PGO_CLANG=y

Clang also supports SamplePGO (-fprofile-sample-use; AutoFDO) and
context-sensitive PGO (post-inline, -fcs-profile-generate).
Context-sensitive SamplePGO is under development.

If the naming does not make adding future other PGO features difficult,
I am happy with CONFIG_PGO_CLANG :)


Aside from the question and the issue above, the description looks good to me.

>+Note that kernels compiled with profiling flags will be significantly larger
>+and run slower.
>+
>+Profiling data will only become accessible once debugfs has been mounted:
>+
>+.. code-block:: sh
>+
>+   mount -t debugfs none /sys/kernel/debug
>+
>+
>+Customization
>+=============
>+
>+You can enable or disable profiling for individual file and directories by
>+adding a line similar to the following to the respective kernel Makefile:
>+
>+- For a single file (e.g. main.o)
>+
>+  .. code-block:: make
>+
>+     PGO_PROFILE_main.o := y
>+
>+- For all files in one directory
>+
>+  .. code-block:: make
>+
>+     PGO_PROFILE := y
>+
>+To exclude files from being profiled use
>+
>+  .. code-block:: make
>+
>+     PGO_PROFILE_main.o := n
>+
>+and
>+
>+  .. code-block:: make
>+
>+     PGO_PROFILE := n
>+
>+Only files which are linked to the main kernel image or are compiled as kernel
>+modules are supported by this mechanism.
>+
>+
>+Files
>+=====
>+
>+The PGO kernel support creates the following files in debugfs:
>+
>+``/sys/kernel/debug/pgo``
>+	Parent directory for all PGO-related files.
>+
>+``/sys/kernel/debug/pgo/reset``
>+	Global reset file: resets all coverage data to zero when written to.
>+
>+``/sys/kernel/debug/profraw``
>+	The raw PGO data that must be processed with ``llvm_profdata``.
>+
>+
>+Workflow
>+========
>+
>+The PGO kernel can be run on the host or test machines. The data though should
>+be analyzed with Clang's tools from the same Clang version as the kernel was
>+compiled. Clang's tolerant of version skew, but it's easier to use the same
>+Clang version.
>+
>+The profiling data is useful for optimizing the kernel, analyzing coverage,
>+etc. Clang offers tools to perform these tasks.
>+
>+Here is an example workflow for profiling an instrumented kernel with PGO and
>+using the result to optimize the kernel:
>+
>+1) Install the kernel on the TEST machine.
>+
>+2) Reset the data counters right before running the load tests
>+
>+   .. code-block:: sh
>+
>+      echo 1 > /sys/kernel/debug/pgo/reset
>+
>+3) Run the load tests.
>+
>+4) Collect the raw profile data
>+
>+   .. code-block:: sh
>+
>+      cp -a /sys/kernel/debug/pgo/profraw /tmp/vmlinux.profraw
>+
>+5) (Optional) Download the raw profile data to the HOST machine.
>+
>+6) Process the raw profile data
>+
>+   .. code-block:: sh
>+
>+      llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
>+
>+   Note that multiple raw profile data files can be merged during this step.
>+
>+7) Rebuild the kernel using the profile data (PGO disabled)
>+
>+   .. code-block:: sh
>+
>+      make ... KCLAGS=-fprofile-use=vmlinux.profdata
>diff --git a/MAINTAINERS b/MAINTAINERS
>index 6390491b07e51..7a98bdaab9861 100644
>--- a/MAINTAINERS
>+++ b/MAINTAINERS
>@@ -13955,6 +13955,15 @@ S:	Maintained
> F:	include/linux/personality.h
> F:	include/uapi/linux/personality.h
>
>+PGO BASED KERNEL PROFILING
>+M:	Sami Tolvanen <samitolvanen@google.com>
>+M:	Bill Wendling <wcw@google.com>
>+R:	Nathan Chancellor <natechancellor@gmail.com>
>+R:	Nick Desaulniers <ndesaulniers@google.com>
>+S:	Supported
>+F:	Documentation/dev-tools/pgo.rst
>+F:	kernel/pgo
>+
> PHOENIX RC FLIGHT CONTROLLER ADAPTER
> M:	Marcus Folkesson <marcus.folkesson@gmail.com>
> L:	linux-input@vger.kernel.org
>diff --git a/Makefile b/Makefile
>index 8b2c3f88ee5ea..4f42957c78134 100644
>--- a/Makefile
>+++ b/Makefile
>@@ -659,6 +659,9 @@ endif # KBUILD_EXTMOD
> # Defaults to vmlinux, but the arch makefile usually adds further targets
> all: vmlinux
>
>+CFLAGS_PGO_CLANG := -fprofile-generate
>+export CFLAGS_PGO_CLANG
>+
> CFLAGS_GCOV	:= -fprofile-arcs -ftest-coverage \
> 	$(call cc-option,-fno-tree-loop-im) \
> 	$(call cc-disable-warning,maybe-uninitialized,)
>diff --git a/arch/Kconfig b/arch/Kconfig
>index 78c6f05b10f91..a7a6ab7d204dc 100644
>--- a/arch/Kconfig
>+++ b/arch/Kconfig
>@@ -1106,6 +1106,7 @@ config ARCH_SUPPORTS_DEBUG_PAGEALLOC
> 	bool
>
> source "kernel/gcov/Kconfig"
>+source "kernel/pgo/Kconfig"
>
> source "scripts/gcc-plugins/Kconfig"
>
>diff --git a/arch/arm/boot/bootp/Makefile b/arch/arm/boot/bootp/Makefile
>index 981a8d03f064c..523bd58df0a4b 100644
>--- a/arch/arm/boot/bootp/Makefile
>+++ b/arch/arm/boot/bootp/Makefile
>@@ -7,6 +7,7 @@
> #
>
> GCOV_PROFILE	:= n
>+PGO_PROFILE	:= n
>
> LDFLAGS_bootp	:= --no-undefined -X \
> 		 --defsym initrd_phys=$(INITRD_PHYS) \
>diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
>index fb521efcc6c20..5fd0fd85fc0e5 100644
>--- a/arch/arm/boot/compressed/Makefile
>+++ b/arch/arm/boot/compressed/Makefile
>@@ -24,6 +24,7 @@ OBJS		+= hyp-stub.o
> endif
>
> GCOV_PROFILE		:= n
>+PGO_PROFILE		:= n
> KASAN_SANITIZE		:= n
>
> # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
>diff --git a/arch/arm/vdso/Makefile b/arch/arm/vdso/Makefile
>index b558bee0e1f6b..11f6ce4b48b56 100644
>--- a/arch/arm/vdso/Makefile
>+++ b/arch/arm/vdso/Makefile
>@@ -36,8 +36,9 @@ else
> CFLAGS_vgettimeofday.o = -O2 -include $(c-gettimeofday-y)
> endif
>
>-# Disable gcov profiling for VDSO code
>+# Disable gcov and PGO profiling for VDSO code
> GCOV_PROFILE := n
>+PGO_PROFILE := n
>
> # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
> KCOV_INSTRUMENT := n
>diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
>index cd9c3fa25902f..d48fc0df07020 100644
>--- a/arch/arm64/kernel/vdso/Makefile
>+++ b/arch/arm64/kernel/vdso/Makefile
>@@ -41,8 +41,9 @@ ifneq ($(c-gettimeofday-y),)
>   CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)
> endif
>
>-# Disable gcov profiling for VDSO code
>+# Disable gcov and PGO profiling for VDSO code
> GCOV_PROFILE := n
>+PGO_PROFILE := n
>
> obj-y += vdso.o
> targets += vdso.lds
>diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
>index 1f1e351c5fe2b..ad128ecdbfbdf 100644
>--- a/arch/arm64/kvm/hyp/nvhe/Makefile
>+++ b/arch/arm64/kvm/hyp/nvhe/Makefile
>@@ -60,6 +60,7 @@ KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS), $(KBUILD_CFLAG
> # compiler instrumentation that inserts callbacks or checks into the code may
> # cause crashes. Just disable it.
> GCOV_PROFILE	:= n
>+PGO_PROFILE	:= n
> KASAN_SANITIZE	:= n
> UBSAN_SANITIZE	:= n
> KCOV_INSTRUMENT	:= n
>diff --git a/arch/mips/boot/compressed/Makefile b/arch/mips/boot/compressed/Makefile
>index 47cd9dc7454af..0855ea12f2c7f 100644
>--- a/arch/mips/boot/compressed/Makefile
>+++ b/arch/mips/boot/compressed/Makefile
>@@ -37,6 +37,7 @@ KBUILD_AFLAGS := $(KBUILD_AFLAGS) -D__ASSEMBLY__ \
> # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
> KCOV_INSTRUMENT		:= n
> GCOV_PROFILE := n
>+PGO_PROFILE := n
>
> # decompressor objects (linked with vmlinuz)
> vmlinuzobjs-y := $(obj)/head.o $(obj)/decompress.o $(obj)/string.o
>diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
>index 5810cc12bc1d9..d7eb64de35eae 100644
>--- a/arch/mips/vdso/Makefile
>+++ b/arch/mips/vdso/Makefile
>@@ -66,6 +66,7 @@ ldflags-y := -Bsymbolic --no-undefined -soname=linux-vdso.so.1 \
> CFLAGS_REMOVE_vdso.o = -pg
>
> GCOV_PROFILE := n
>+PGO_PROFILE := n
> UBSAN_SANITIZE := n
> KCOV_INSTRUMENT := n
>
>diff --git a/arch/nds32/kernel/vdso/Makefile b/arch/nds32/kernel/vdso/Makefile
>index 55df25ef00578..f2b53ee2124b7 100644
>--- a/arch/nds32/kernel/vdso/Makefile
>+++ b/arch/nds32/kernel/vdso/Makefile
>@@ -15,9 +15,9 @@ obj-vdso := $(addprefix $(obj)/, $(obj-vdso))
> ccflags-y := -shared -fno-common -fno-builtin -nostdlib -fPIC -Wl,-shared -g \
> 	-Wl,-soname=linux-vdso.so.1 -Wl,--hash-style=sysv
>
>-# Disable gcov profiling for VDSO code
>+# Disable gcov and PGO profiling for VDSO code
> GCOV_PROFILE := n
>-
>+PGO_PROFILE := n
>
> obj-y += vdso.o
> targets += vdso.lds
>diff --git a/arch/parisc/boot/compressed/Makefile b/arch/parisc/boot/compressed/Makefile
>index dff4536875305..5cf93a67f7da7 100644
>--- a/arch/parisc/boot/compressed/Makefile
>+++ b/arch/parisc/boot/compressed/Makefile
>@@ -7,6 +7,7 @@
>
> KCOV_INSTRUMENT := n
> GCOV_PROFILE := n
>+PGO_PROFILE := n
> UBSAN_SANITIZE := n
>
> targets := vmlinux.lds vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2
>diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
>index fe2ef598e2ead..c642c046660d7 100644
>--- a/arch/powerpc/kernel/Makefile
>+++ b/arch/powerpc/kernel/Makefile
>@@ -153,17 +153,21 @@ endif
> obj-$(CONFIG_PPC_SECURE_BOOT)	+= secure_boot.o ima_arch.o secvar-ops.o
> obj-$(CONFIG_PPC_SECVAR_SYSFS)	+= secvar-sysfs.o
>
>-# Disable GCOV, KCOV & sanitizers in odd or sensitive code
>+# Disable GCOV, PGO, KCOV & sanitizers in odd or sensitive code
> GCOV_PROFILE_prom_init.o := n
>+PGO_PROFILE_prom_init.o := n
> KCOV_INSTRUMENT_prom_init.o := n
> UBSAN_SANITIZE_prom_init.o := n
> GCOV_PROFILE_kprobes.o := n
>+PGO_PROFILE_kprobes.o := n
> KCOV_INSTRUMENT_kprobes.o := n
> UBSAN_SANITIZE_kprobes.o := n
> GCOV_PROFILE_kprobes-ftrace.o := n
>+PGO_PROFILE_kprobes-ftrace.o := n
> KCOV_INSTRUMENT_kprobes-ftrace.o := n
> UBSAN_SANITIZE_kprobes-ftrace.o := n
> GCOV_PROFILE_syscall_64.o := n
>+PGO_PROFILE_syscall_64.o := n
> KCOV_INSTRUMENT_syscall_64.o := n
> UBSAN_SANITIZE_syscall_64.o := n
> UBSAN_SANITIZE_vdso.o := n
>diff --git a/arch/powerpc/kernel/trace/Makefile b/arch/powerpc/kernel/trace/Makefile
>index 858503775c583..7d72ae7d4f8c6 100644
>--- a/arch/powerpc/kernel/trace/Makefile
>+++ b/arch/powerpc/kernel/trace/Makefile
>@@ -23,7 +23,8 @@ obj-$(CONFIG_TRACING)			+= trace_clock.o
> obj-$(CONFIG_PPC64)			+= $(obj64-y)
> obj-$(CONFIG_PPC32)			+= $(obj32-y)
>
>-# Disable GCOV, KCOV & sanitizers in odd or sensitive code
>+# Disable GCOV, PGO, KCOV & sanitizers in odd or sensitive code
> GCOV_PROFILE_ftrace.o := n
>+PGO_PROFILE_ftrace.o := n
> KCOV_INSTRUMENT_ftrace.o := n
> UBSAN_SANITIZE_ftrace.o := n
>diff --git a/arch/powerpc/kernel/vdso32/Makefile b/arch/powerpc/kernel/vdso32/Makefile
>index 9cb6f524854b9..655e159975a04 100644
>--- a/arch/powerpc/kernel/vdso32/Makefile
>+++ b/arch/powerpc/kernel/vdso32/Makefile
>@@ -34,6 +34,7 @@ targets := $(obj-vdso32) vdso32.so.dbg
> obj-vdso32 := $(addprefix $(obj)/, $(obj-vdso32))
>
> GCOV_PROFILE := n
>+PGO_PROFILE := n
> KCOV_INSTRUMENT := n
> UBSAN_SANITIZE := n
> KASAN_SANITIZE := n
>diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile
>index bf363ff371521..12c286f5afc16 100644
>--- a/arch/powerpc/kernel/vdso64/Makefile
>+++ b/arch/powerpc/kernel/vdso64/Makefile
>@@ -21,6 +21,7 @@ targets := $(obj-vdso64) vdso64.so.dbg
> obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64))
>
> GCOV_PROFILE := n
>+PGO_PROFILE := n
> KCOV_INSTRUMENT := n
> UBSAN_SANITIZE := n
> KASAN_SANITIZE := n
>diff --git a/arch/powerpc/kexec/Makefile b/arch/powerpc/kexec/Makefile
>index 4aff6846c7726..1c7f65e3cb969 100644
>--- a/arch/powerpc/kexec/Makefile
>+++ b/arch/powerpc/kexec/Makefile
>@@ -16,7 +16,8 @@ endif
> endif
>
>
>-# Disable GCOV, KCOV & sanitizers in odd or sensitive code
>+# Disable GCOV, PGO, KCOV & sanitizers in odd or sensitive code
> GCOV_PROFILE_core_$(BITS).o := n
>+PGO_PROFILE_core_$(BITS).o := n
> KCOV_INSTRUMENT_core_$(BITS).o := n
> UBSAN_SANITIZE_core_$(BITS).o := n
>diff --git a/arch/powerpc/xmon/Makefile b/arch/powerpc/xmon/Makefile
>index eb25d7554ffd1..7aff80d18b44b 100644
>--- a/arch/powerpc/xmon/Makefile
>+++ b/arch/powerpc/xmon/Makefile
>@@ -2,6 +2,7 @@
> # Makefile for xmon
>
> GCOV_PROFILE := n
>+PGO_PROFILE := n
> KCOV_INSTRUMENT := n
> UBSAN_SANITIZE := n
> KASAN_SANITIZE := n
>diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
>index 0cfd6da784f84..882340dc3c647 100644
>--- a/arch/riscv/kernel/vdso/Makefile
>+++ b/arch/riscv/kernel/vdso/Makefile
>@@ -32,8 +32,9 @@ CPPFLAGS_vdso.lds += -P -C -U$(ARCH)
> # Disable -pg to prevent insert call site
> CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os
>
>-# Disable gcov profiling for VDSO code
>+# Disable gcov and PGO profiling for VDSO code
> GCOV_PROFILE := n
>+PGO_PROFILE := n
> KCOV_INSTRUMENT := n
>
> # Force dependency
>diff --git a/arch/s390/boot/Makefile b/arch/s390/boot/Makefile
>index 41a64b8dce252..bee4a32040e79 100644
>--- a/arch/s390/boot/Makefile
>+++ b/arch/s390/boot/Makefile
>@@ -5,6 +5,7 @@
>
> KCOV_INSTRUMENT := n
> GCOV_PROFILE := n
>+PGO_PROFILE := n
> UBSAN_SANITIZE := n
> KASAN_SANITIZE := n
>
>diff --git a/arch/s390/boot/compressed/Makefile b/arch/s390/boot/compressed/Makefile
>index de18dab518bb6..c3ab883e8425a 100644
>--- a/arch/s390/boot/compressed/Makefile
>+++ b/arch/s390/boot/compressed/Makefile
>@@ -7,6 +7,7 @@
>
> KCOV_INSTRUMENT := n
> GCOV_PROFILE := n
>+PGO_PROFILE := n
> UBSAN_SANITIZE := n
> KASAN_SANITIZE := n
>
>diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile
>index dd73b7f074237..bd857aacad794 100644
>--- a/arch/s390/kernel/Makefile
>+++ b/arch/s390/kernel/Makefile
>@@ -14,6 +14,7 @@ CFLAGS_REMOVE_early.o		= $(CC_FLAGS_FTRACE)
> endif
>
> GCOV_PROFILE_early.o		:= n
>+PGO_PROFILE_early.o		:= n
> KCOV_INSTRUMENT_early.o		:= n
> UBSAN_SANITIZE_early.o		:= n
> KASAN_SANITIZE_ipl.o		:= n
>diff --git a/arch/s390/kernel/vdso64/Makefile b/arch/s390/kernel/vdso64/Makefile
>index a6e0fb6b91d6c..d7c43b7c1db96 100644
>--- a/arch/s390/kernel/vdso64/Makefile
>+++ b/arch/s390/kernel/vdso64/Makefile
>@@ -35,8 +35,9 @@ obj-y += vdso64_wrapper.o
> targets += vdso64.lds
> CPPFLAGS_vdso64.lds += -P -C -U$(ARCH)
>
>-# Disable gcov profiling, ubsan and kasan for VDSO code
>+# Disable gcov and PGO profiling, ubsan and kasan for VDSO code
> GCOV_PROFILE := n
>+PGO_PROFILE := n
> UBSAN_SANITIZE := n
> KASAN_SANITIZE := n
>
>diff --git a/arch/s390/purgatory/Makefile b/arch/s390/purgatory/Makefile
>index c57f8c40e9926..9aef584e98466 100644
>--- a/arch/s390/purgatory/Makefile
>+++ b/arch/s390/purgatory/Makefile
>@@ -17,6 +17,7 @@ $(obj)/mem.o: $(srctree)/arch/s390/lib/mem.S FORCE
>
> KCOV_INSTRUMENT := n
> GCOV_PROFILE := n
>+PGO_PROFILE := n
> UBSAN_SANITIZE := n
> KASAN_SANITIZE := n
>
>diff --git a/arch/sh/boot/compressed/Makefile b/arch/sh/boot/compressed/Makefile
>index 589d2d8a573db..ae19aeeb3964c 100644
>--- a/arch/sh/boot/compressed/Makefile
>+++ b/arch/sh/boot/compressed/Makefile
>@@ -13,6 +13,7 @@ targets		:= vmlinux vmlinux.bin vmlinux.bin.gz \
> OBJECTS = $(obj)/head_32.o $(obj)/misc.o $(obj)/cache.o
>
> GCOV_PROFILE := n
>+PGO_PROFILE := n
>
> #
> # IMAGE_OFFSET is the load offset of the compression loader
>diff --git a/arch/sh/mm/Makefile b/arch/sh/mm/Makefile
>index f69ddc70b1465..ea2782c631f43 100644
>--- a/arch/sh/mm/Makefile
>+++ b/arch/sh/mm/Makefile
>@@ -43,3 +43,4 @@ obj-$(CONFIG_UNCACHED_MAPPING)	+= uncached.o
> obj-$(CONFIG_HAVE_SRAM_POOL)	+= sram.o
>
> GCOV_PROFILE_pmb.o := n
>+PGO_PROFILE_pmb.o := n
>diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile
>index c5e1545bc5cf9..ab5f3783fe199 100644
>--- a/arch/sparc/vdso/Makefile
>+++ b/arch/sparc/vdso/Makefile
>@@ -115,6 +115,7 @@ quiet_cmd_vdso = VDSO    $@
>
> VDSO_LDFLAGS = -shared --hash-style=both --build-id=sha1 -Bsymbolic
> GCOV_PROFILE := n
>+PGO_PROFILE := n
>
> #
> # Install the unstripped copies of vdso*.so.  If our toolchain supports
>diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>index 7b6dd10b162ac..a751b4f8f6645 100644
>--- a/arch/x86/Kconfig
>+++ b/arch/x86/Kconfig
>@@ -95,6 +95,7 @@ config X86
> 	select ARCH_SUPPORTS_DEBUG_PAGEALLOC
> 	select ARCH_SUPPORTS_NUMA_BALANCING	if X86_64
> 	select ARCH_SUPPORTS_KMAP_LOCAL_FORCE_MAP	if NR_CPUS <= 4096
>+	select ARCH_SUPPORTS_PGO_CLANG		if X86_64
> 	select ARCH_USE_BUILTIN_BSWAP
> 	select ARCH_USE_QUEUED_RWLOCKS
> 	select ARCH_USE_QUEUED_SPINLOCKS
>diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
>index fe605205b4ce2..383853e32f673 100644
>--- a/arch/x86/boot/Makefile
>+++ b/arch/x86/boot/Makefile
>@@ -71,6 +71,7 @@ KBUILD_AFLAGS	:= $(KBUILD_CFLAGS) -D__ASSEMBLY__
> KBUILD_CFLAGS	+= $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
> KBUILD_CFLAGS	+= -fno-asynchronous-unwind-tables
> GCOV_PROFILE := n
>+PGO_PROFILE := n
> UBSAN_SANITIZE := n
>
> $(obj)/bzImage: asflags-y  := $(SVGA_MODE)
>diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
>index e0bc3988c3faa..ed12ab65f6065 100644
>--- a/arch/x86/boot/compressed/Makefile
>+++ b/arch/x86/boot/compressed/Makefile
>@@ -54,6 +54,7 @@ CFLAGS_sev-es.o += -I$(objtree)/arch/x86/lib/
>
> KBUILD_AFLAGS  := $(KBUILD_CFLAGS) -D__ASSEMBLY__
> GCOV_PROFILE := n
>+PGO_PROFILE := n
> UBSAN_SANITIZE :=n
>
> KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
>diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
>index 02e3e42f380bd..26e2b3af0145c 100644
>--- a/arch/x86/entry/vdso/Makefile
>+++ b/arch/x86/entry/vdso/Makefile
>@@ -179,6 +179,7 @@ quiet_cmd_vdso = VDSO    $@
> VDSO_LDFLAGS = -shared --hash-style=both --build-id=sha1 \
> 	$(call ld-option, --eh-frame-hdr) -Bsymbolic
> GCOV_PROFILE := n
>+PGO_PROFILE := n
>
> quiet_cmd_vdso_and_check = VDSO    $@
>       cmd_vdso_and_check = $(cmd_vdso); $(cmd_vdso_check)
>diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
>index efd9e9ea17f25..f6cab2316c46a 100644
>--- a/arch/x86/kernel/vmlinux.lds.S
>+++ b/arch/x86/kernel/vmlinux.lds.S
>@@ -184,6 +184,8 @@ SECTIONS
>
> 	BUG_TABLE
>
>+	PGO_CLANG_DATA
>+
> 	ORC_UNWIND_TABLE
>
> 	. = ALIGN(PAGE_SIZE);
>diff --git a/arch/x86/platform/efi/Makefile b/arch/x86/platform/efi/Makefile
>index 84b09c230cbd5..5f22b31446ad4 100644
>--- a/arch/x86/platform/efi/Makefile
>+++ b/arch/x86/platform/efi/Makefile
>@@ -2,6 +2,7 @@
> OBJECT_FILES_NON_STANDARD_efi_thunk_$(BITS).o := y
> KASAN_SANITIZE := n
> GCOV_PROFILE := n
>+PGO_PROFILE := n
>
> obj-$(CONFIG_EFI) 		+= quirks.o efi.o efi_$(BITS).o efi_stub_$(BITS).o
> obj-$(CONFIG_EFI_MIXED)		+= efi_thunk_$(BITS).o
>diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
>index 95ea17a9d20cb..36f20e99da0bc 100644
>--- a/arch/x86/purgatory/Makefile
>+++ b/arch/x86/purgatory/Makefile
>@@ -23,6 +23,7 @@ targets += purgatory.ro purgatory.chk
>
> # Sanitizer, etc. runtimes are unavailable and cannot be linked here.
> GCOV_PROFILE	:= n
>+PGO_PROFILE	:= n
> KASAN_SANITIZE	:= n
> UBSAN_SANITIZE	:= n
> KCSAN_SANITIZE	:= n
>diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile
>index 83f1b6a56449f..21797192f958f 100644
>--- a/arch/x86/realmode/rm/Makefile
>+++ b/arch/x86/realmode/rm/Makefile
>@@ -76,4 +76,5 @@ KBUILD_CFLAGS	:= $(REALMODE_CFLAGS) -D_SETUP -D_WAKEUP \
> KBUILD_AFLAGS	:= $(KBUILD_CFLAGS) -D__ASSEMBLY__
> KBUILD_CFLAGS	+= -fno-asynchronous-unwind-tables
> GCOV_PROFILE := n
>+PGO_PROFILE := n
> UBSAN_SANITIZE := n
>diff --git a/arch/x86/um/vdso/Makefile b/arch/x86/um/vdso/Makefile
>index 5943387e3f357..54f5768f58530 100644
>--- a/arch/x86/um/vdso/Makefile
>+++ b/arch/x86/um/vdso/Makefile
>@@ -64,6 +64,7 @@ quiet_cmd_vdso = VDSO    $@
>
> VDSO_LDFLAGS = -fPIC -shared -Wl,--hash-style=sysv
> GCOV_PROFILE := n
>+PGO_PROFILE := n
>
> #
> # Install the unstripped copy of vdso*.so listed in $(vdso-install-y).
>diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
>index 8a94388e38b33..2d81623b33f29 100644
>--- a/drivers/firmware/efi/libstub/Makefile
>+++ b/drivers/firmware/efi/libstub/Makefile
>@@ -40,6 +40,7 @@ KBUILD_CFLAGS			:= $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
> KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))
>
> GCOV_PROFILE			:= n
>+PGO_PROFILE			:= n
> # Sanitizer runtimes are unavailable and cannot be linked here.
> KASAN_SANITIZE			:= n
> KCSAN_SANITIZE			:= n
>diff --git a/drivers/s390/char/Makefile b/drivers/s390/char/Makefile
>index c6fdb81a068a6..bf6c5db5da1fc 100644
>--- a/drivers/s390/char/Makefile
>+++ b/drivers/s390/char/Makefile
>@@ -9,6 +9,7 @@ CFLAGS_REMOVE_sclp_early_core.o	= $(CC_FLAGS_FTRACE)
> endif
>
> GCOV_PROFILE_sclp_early_core.o		:= n
>+PGO_PROFILE_sclp_early_core.o		:= n
> KCOV_INSTRUMENT_sclp_early_core.o	:= n
> UBSAN_SANITIZE_sclp_early_core.o	:= n
> KASAN_SANITIZE_sclp_early_core.o	:= n
>diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
>index b2b3d81b1535a..3a591bb18c5fb 100644
>--- a/include/asm-generic/vmlinux.lds.h
>+++ b/include/asm-generic/vmlinux.lds.h
>@@ -316,6 +316,49 @@
> #define THERMAL_TABLE(name)
> #endif
>
>+#ifdef CONFIG_PGO_CLANG
>+#define PGO_CLANG_DATA							\
>+	__llvm_prf_data : AT(ADDR(__llvm_prf_data) - LOAD_OFFSET) {	\
>+		. = ALIGN(8);						\
>+		__llvm_prf_start = .;					\
>+		__llvm_prf_data_start = .;				\
>+		KEEP(*(__llvm_prf_data))				\
>+		. = ALIGN(8);						\
>+		__llvm_prf_data_end = .;				\
>+	}								\
>+	__llvm_prf_cnts : AT(ADDR(__llvm_prf_cnts) - LOAD_OFFSET) {	\
>+		. = ALIGN(8);						\
>+		__llvm_prf_cnts_start = .;				\
>+		KEEP(*(__llvm_prf_cnts))				\
>+		. = ALIGN(8);						\
>+		__llvm_prf_cnts_end = .;				\
>+	}								\
>+	__llvm_prf_names : AT(ADDR(__llvm_prf_names) - LOAD_OFFSET) {	\
>+		. = ALIGN(8);						\
>+		__llvm_prf_names_start = .;				\
>+		KEEP(*(__llvm_prf_names))				\
>+		. = ALIGN(8);						\
>+		__llvm_prf_names_end = .;				\
>+		. = ALIGN(8);						\
>+	}								\
>+	__llvm_prf_vals : AT(ADDR(__llvm_prf_vals) - LOAD_OFFSET) {	\
>+		__llvm_prf_vals_start = .;				\
>+		KEEP(*(__llvm_prf_vals))				\
>+		. = ALIGN(8);						\
>+		__llvm_prf_vals_end = .;				\
>+		. = ALIGN(8);						\
>+	}								\
>+	__llvm_prf_vnds : AT(ADDR(__llvm_prf_vnds) - LOAD_OFFSET) {	\
>+		__llvm_prf_vnds_start = .;				\
>+		KEEP(*(__llvm_prf_vnds))				\
>+		. = ALIGN(8);						\
>+		__llvm_prf_vnds_end = .;				\
>+		__llvm_prf_end = .;					\
>+	}
>+#else
>+#define PGO_CLANG_DATA
>+#endif
>+
> #define KERNEL_DTB()							\
> 	STRUCT_ALIGN();							\
> 	__dtb_start = .;						\
>@@ -1125,6 +1168,7 @@
> 		CONSTRUCTORS						\
> 	}								\
> 	BUG_TABLE							\
>+	PGO_CLANG_DATA
>
> #define INIT_TEXT_SECTION(inittext_align)				\
> 	. = ALIGN(inittext_align);					\
>diff --git a/kernel/Makefile b/kernel/Makefile
>index aa7368c7eabf3..0b34ca228ba46 100644
>--- a/kernel/Makefile
>+++ b/kernel/Makefile
>@@ -111,6 +111,7 @@ obj-$(CONFIG_BPF) += bpf/
> obj-$(CONFIG_KCSAN) += kcsan/
> obj-$(CONFIG_SHADOW_CALL_STACK) += scs.o
> obj-$(CONFIG_HAVE_STATIC_CALL_INLINE) += static_call.o
>+obj-$(CONFIG_PGO_CLANG) += pgo/
>
> obj-$(CONFIG_PERF_EVENTS) += events/
>
>diff --git a/kernel/pgo/Kconfig b/kernel/pgo/Kconfig
>new file mode 100644
>index 0000000000000..318d36bb3d106
>--- /dev/null
>+++ b/kernel/pgo/Kconfig
>@@ -0,0 +1,34 @@
>+# SPDX-License-Identifier: GPL-2.0-only
>+menu "Profile Guided Optimization (PGO) (EXPERIMENTAL)"
>+
>+config ARCH_SUPPORTS_PGO_CLANG
>+	bool
>+
>+config PGO_CLANG
>+	bool "Enable clang's PGO-based kernel profiling"
>+	depends on DEBUG_FS
>+	depends on ARCH_SUPPORTS_PGO_CLANG
>+	help
>+	  This option enables clang's PGO (Profile Guided Optimization) based
>+	  code profiling to better optimize the kernel.
>+
>+	  If unsure, say N.
>+
>+	  Run a representative workload for your application on a kernel
>+	  compiled with this option and download the raw profile file from
>+	  /sys/kernel/debug/pgo/profraw. This file needs to be processed with
>+	  llvm-profdata. It may be merged with other collected raw profiles.
>+
>+	  Copy the resulting profile file into vmlinux.profdata, and enable
>+	  KCFLAGS=-fprofile-use=vmlinux.profdata to produce an optimized
>+	  kernel.
>+
>+	  Note that a kernel compiled with profiling flags will be
>+	  significatnly larger and run slower. Also be sure to exclude files
>+	  from profiling which are not linked to the kernel image to prevent
>+	  linker errors.
>+
>+	  Note that the debugfs filesystem has to be mounted to access
>+	  profiling data.
>+
>+endmenu
>diff --git a/kernel/pgo/Makefile b/kernel/pgo/Makefile
>new file mode 100644
>index 0000000000000..41e27cefd9a47
>--- /dev/null
>+++ b/kernel/pgo/Makefile
>@@ -0,0 +1,5 @@
>+# SPDX-License-Identifier: GPL-2.0
>+GCOV_PROFILE	:= n
>+PGO_PROFILE	:= n
>+
>+obj-y	+= fs.o instrument.o
>diff --git a/kernel/pgo/fs.c b/kernel/pgo/fs.c
>new file mode 100644
>index 0000000000000..790a8df037bfc
>--- /dev/null
>+++ b/kernel/pgo/fs.c
>@@ -0,0 +1,382 @@
>+// SPDX-License-Identifier: GPL-2.0
>+/*
>+ * Copyright (C) 2019 Google, Inc.
>+ *
>+ * Author:
>+ *	Sami Tolvanen <samitolvanen@google.com>
>+ *
>+ * This software is licensed under the terms of the GNU General Public
>+ * License version 2, as published by the Free Software Foundation, and
>+ * may be copied, distributed, and modified under those terms.
>+ *
>+ * This program is distributed in the hope that it will be useful,
>+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
>+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>+ * GNU General Public License for more details.
>+ *
>+ */
>+
>+#define pr_fmt(fmt)	"pgo: " fmt
>+
>+#include <linux/kernel.h>
>+#include <linux/debugfs.h>
>+#include <linux/fs.h>
>+#include <linux/module.h>
>+#include <linux/slab.h>
>+#include <linux/vmalloc.h>
>+#include "pgo.h"
>+
>+static struct dentry *directory;
>+
>+struct prf_private_data {
>+	void *buffer;
>+	unsigned long size;
>+};
>+
>+/*
>+ * Raw profile data format:
>+ *
>+ *	- llvm_prf_header
>+ *	- __llvm_prf_data
>+ *	- __llvm_prf_cnts
>+ *	- __llvm_prf_names
>+ *	- zero padding to 8 bytes
>+ *	- for each llvm_prf_data in __llvm_prf_data:
>+ *		- llvm_prf_value_data
>+ *			- llvm_prf_value_record + site count array
>+ *				- llvm_prf_value_node_data
>+ *				...
>+ *			...
>+ *		...
>+ */
>+
>+static void prf_fill_header(void **buffer)
>+{
>+	struct llvm_prf_header *header = *(struct llvm_prf_header **)buffer;
>+
>+	header->magic = LLVM_PRF_MAGIC;
>+	header->version = LLVM_PRF_VARIANT_MASK_IR | LLVM_PRF_VERSION;
>+	header->data_size = prf_data_count();
>+	header->padding_bytes_before_counters = 0;
>+	header->counters_size = prf_cnts_count();
>+	header->padding_bytes_after_counters = 0;
>+	header->names_size = prf_names_count();
>+	header->counters_delta = (u64)__llvm_prf_cnts_start;
>+	header->names_delta = (u64)__llvm_prf_names_start;
>+	header->value_kind_last = LLVM_PRF_IPVK_LAST;
>+
>+	*buffer += sizeof(*header);
>+}
>+
>+/*
>+ * Copy the source into the buffer, incrementing the pointer into buffer in the
>+ * process.
>+ */
>+static void prf_copy_to_buffer(void **buffer, void *src, unsigned long size)
>+{
>+	memcpy(*buffer, src, size);
>+	*buffer += size;
>+}
>+
>+static u32 __prf_get_value_size(struct llvm_prf_data *p, u32 *value_kinds)
>+{
>+	struct llvm_prf_value_node **nodes =
>+		(struct llvm_prf_value_node **)p->values;
>+	u32 kinds = 0;
>+	u32 size = 0;
>+	unsigned int kind;
>+	unsigned int n;
>+	unsigned int s = 0;
>+
>+	for (kind = 0; kind < ARRAY_SIZE(p->num_value_sites); kind++) {
>+		unsigned int sites = p->num_value_sites[kind];
>+
>+		if (!sites)
>+			continue;
>+
>+		/* Record + site count array */
>+		size += prf_get_value_record_size(sites);
>+		kinds++;
>+
>+		if (!nodes)
>+			continue;
>+
>+		for (n = 0; n < sites; n++) {
>+			u32 count = 0;
>+			struct llvm_prf_value_node *site = nodes[s + n];
>+
>+			while (site && ++count <= U8_MAX)
>+				site = site->next;
>+
>+			size += count *
>+				sizeof(struct llvm_prf_value_node_data);
>+		}
>+
>+		s += sites;
>+	}
>+
>+	if (size)
>+		size += sizeof(struct llvm_prf_value_data);
>+
>+	if (value_kinds)
>+		*value_kinds = kinds;
>+
>+	return size;
>+}
>+
>+static u32 prf_get_value_size(void)
>+{
>+	u32 size = 0;
>+	struct llvm_prf_data *p;
>+
>+	for (p = __llvm_prf_data_start; p < __llvm_prf_data_end; p++)
>+		size += __prf_get_value_size(p, NULL);
>+
>+	return size;
>+}
>+
>+/* Serialize the profiling's value. */
>+static void prf_serialize_value(struct llvm_prf_data *p, void **buffer)
>+{
>+	struct llvm_prf_value_data header;
>+	struct llvm_prf_value_node **nodes =
>+		(struct llvm_prf_value_node **)p->values;
>+	unsigned int kind;
>+	unsigned int n;
>+	unsigned int s = 0;
>+
>+	header.total_size = __prf_get_value_size(p, &header.num_value_kinds);
>+
>+	if (!header.num_value_kinds)
>+		/* Nothing to write. */
>+		return;
>+
>+	prf_copy_to_buffer(buffer, &header, sizeof(header));
>+
>+	for (kind = 0; kind < ARRAY_SIZE(p->num_value_sites); kind++) {
>+		struct llvm_prf_value_record *record;
>+		u8 *counts;
>+		unsigned int sites = p->num_value_sites[kind];
>+
>+		if (!sites)
>+			continue;
>+
>+		/* Profiling value record. */
>+		record = *(struct llvm_prf_value_record **)buffer;
>+		*buffer += prf_get_value_record_header_size();
>+
>+		record->kind = kind;
>+		record->num_value_sites = sites;
>+
>+		/* Site count array. */
>+		counts = *(u8 **)buffer;
>+		*buffer += prf_get_value_record_site_count_size(sites);
>+
>+		/*
>+		 * If we don't have nodes, we can skip updating the site count
>+		 * array, because the buffer is zero filled.
>+		 */
>+		if (!nodes)
>+			continue;
>+
>+		for (n = 0; n < sites; n++) {
>+			u32 count = 0;
>+			struct llvm_prf_value_node *site = nodes[s + n];
>+
>+			while (site && ++count <= U8_MAX) {
>+				prf_copy_to_buffer(buffer, site,
>+						   sizeof(struct llvm_prf_value_node_data));
>+				site = site->next;
>+			}
>+
>+			counts[n] = (u8)count;
>+		}
>+
>+		s += sites;
>+	}
>+}
>+
>+static void prf_serialize_values(void **buffer)
>+{
>+	struct llvm_prf_data *p;
>+
>+	for (p = __llvm_prf_data_start; p < __llvm_prf_data_end; p++)
>+		prf_serialize_value(p, buffer);
>+}
>+
>+static inline unsigned long prf_get_padding(unsigned long size)
>+{
>+	return 8 - (size % 8);
>+}
>+
>+static unsigned long prf_buffer_size(void)
>+{
>+	return sizeof(struct llvm_prf_header) +
>+			prf_data_size()	+
>+			prf_cnts_size() +
>+			prf_names_size() +
>+			prf_get_padding(prf_names_size()) +
>+			prf_get_value_size();
>+}
>+
>+/* Serialize the profling data into a format LLVM's tools can understand. */
>+static int prf_serialize(struct prf_private_data *p)
>+{
>+	int err = 0;
>+	void *buffer;
>+
>+	p->size = prf_buffer_size();
>+	p->buffer = vzalloc(p->size);
>+
>+	if (!p->buffer) {
>+		err = -ENOMEM;
>+		goto out;
>+	}
>+
>+	buffer = p->buffer;
>+
>+	prf_fill_header(&buffer);
>+	prf_copy_to_buffer(&buffer, __llvm_prf_data_start,  prf_data_size());
>+	prf_copy_to_buffer(&buffer, __llvm_prf_cnts_start,  prf_cnts_size());
>+	prf_copy_to_buffer(&buffer, __llvm_prf_names_start, prf_names_size());
>+	buffer += prf_get_padding(prf_names_size());
>+
>+	prf_serialize_values(&buffer);
>+
>+out:
>+	return err;
>+}
>+
>+/* open() implementation for PGO. Creates a copy of the profiling data set. */
>+static int prf_open(struct inode *inode, struct file *file)
>+{
>+	struct prf_private_data *data;
>+	unsigned long flags;
>+	int err;
>+
>+	data = kzalloc(sizeof(*data), GFP_KERNEL);
>+	if (!data) {
>+		err = -ENOMEM;
>+		goto out;
>+	}
>+
>+	flags = prf_lock();
>+
>+	err = prf_serialize(data);
>+	if (err) {
>+		kfree(data);
>+		goto out_unlock;
>+	}
>+
>+	file->private_data = data;
>+
>+out_unlock:
>+	prf_unlock(flags);
>+out:
>+	return err;
>+}
>+
>+/* read() implementation for PGO. */
>+static ssize_t prf_read(struct file *file, char __user *buf, size_t count,
>+			loff_t *ppos)
>+{
>+	struct prf_private_data *data = file->private_data;
>+
>+	BUG_ON(!data);
>+
>+	return simple_read_from_buffer(buf, count, ppos, data->buffer,
>+				       data->size);
>+}
>+
>+/* release() implementation for PGO. Release resources allocated by open(). */
>+static int prf_release(struct inode *inode, struct file *file)
>+{
>+	struct prf_private_data *data = file->private_data;
>+
>+	if (data) {
>+		vfree(data->buffer);
>+		kfree(data);
>+	}
>+
>+	return 0;
>+}
>+
>+static const struct file_operations prf_fops = {
>+	.owner		= THIS_MODULE,
>+	.open		= prf_open,
>+	.read		= prf_read,
>+	.llseek		= default_llseek,
>+	.release	= prf_release
>+};
>+
>+/* write() implementation for resetting PGO's profile data. */
>+static ssize_t reset_write(struct file *file, const char __user *addr,
>+			   size_t len, loff_t *pos)
>+{
>+	struct llvm_prf_data *data;
>+
>+	memset(__llvm_prf_cnts_start, 0, prf_cnts_size());
>+
>+	for (data = __llvm_prf_data_start; data < __llvm_prf_data_end; ++data) {
>+		struct llvm_prf_value_node **vnodes;
>+		u64 current_vsite_count;
>+		u32 i;
>+
>+		if (!data->values)
>+			continue;
>+
>+		current_vsite_count = 0;
>+		vnodes = (struct llvm_prf_value_node **)data->values;
>+
>+		for (i = LLVM_PRF_IPVK_FIRST; i <= LLVM_PRF_IPVK_LAST; ++i)
>+			current_vsite_count += data->num_value_sites[i];
>+
>+		for (i = 0; i < current_vsite_count; ++i) {
>+			struct llvm_prf_value_node *current_vnode = vnodes[i];
>+
>+			while (current_vnode) {
>+				current_vnode->count = 0;
>+				current_vnode = current_vnode->next;
>+			}
>+		}
>+	}
>+
>+	return len;
>+}
>+
>+static const struct file_operations prf_reset_fops = {
>+	.owner		= THIS_MODULE,
>+	.write		= reset_write,
>+	.llseek		= noop_llseek,
>+};
>+
>+/* Create debugfs entries. */
>+static int __init pgo_init(void)
>+{
>+	directory = debugfs_create_dir("pgo", NULL);
>+	if (!directory)
>+		goto err_remove;
>+
>+	if (!debugfs_create_file("profraw", 0600, directory, NULL,
>+				 &prf_fops))
>+		goto err_remove;
>+
>+	if (!debugfs_create_file("reset", 0200, directory, NULL,
>+				 &prf_reset_fops))
>+		goto err_remove;
>+
>+	return 0;
>+
>+err_remove:
>+	pr_err("initialization failed\n");
>+	return -EIO;
>+}
>+
>+/* Remove debufs entries. */
>+static void __exit pgo_exit(void)
>+{
>+	debugfs_remove_recursive(directory);
>+}
>+
>+module_init(pgo_init);
>+module_exit(pgo_exit);
>diff --git a/kernel/pgo/instrument.c b/kernel/pgo/instrument.c
>new file mode 100644
>index 0000000000000..d96b61a1cf712
>--- /dev/null
>+++ b/kernel/pgo/instrument.c
>@@ -0,0 +1,147 @@
>+// SPDX-License-Identifier: GPL-2.0
>+/*
>+ * Copyright (C) 2019 Google, Inc.
>+ *
>+ * Author:
>+ *	Sami Tolvanen <samitolvanen@google.com>
>+ *
>+ * This software is licensed under the terms of the GNU General Public
>+ * License version 2, as published by the Free Software Foundation, and
>+ * may be copied, distributed, and modified under those terms.
>+ *
>+ * This program is distributed in the hope that it will be useful,
>+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
>+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>+ * GNU General Public License for more details.
>+ *
>+ */
>+
>+#define pr_fmt(fmt)	"pgo: " fmt
>+
>+#include <linux/kernel.h>
>+#include <linux/export.h>
>+#include <linux/spinlock.h>
>+#include <linux/types.h>
>+#include "pgo.h"
>+
>+/* Lock guarding value node access and serialization. */
>+static DEFINE_SPINLOCK(pgo_lock);
>+static int current_node;
>+
>+unsigned long prf_lock(void)
>+{
>+	unsigned long flags;
>+
>+	spin_lock_irqsave(&pgo_lock, flags);
>+
>+	return flags;
>+}
>+
>+void prf_unlock(unsigned long flags)
>+{
>+	spin_unlock_irqrestore(&pgo_lock, flags);
>+}
>+
>+/*
>+ * Return a newly allocated profiling value node which contains the tracked
>+ * value by the value profiler.
>+ * Note: caller *must* hold pgo_lock.
>+ */
>+static struct llvm_prf_value_node *allocate_node(struct llvm_prf_data *p,
>+						 u32 index, u64 value)
>+{
>+	if (&__llvm_prf_vnds_start[current_node + 1] >= __llvm_prf_vnds_end)
>+		return NULL; /* Out of nodes */
>+
>+	current_node++;
>+
>+	/* Make sure the node is entirely within the section */
>+	if (&__llvm_prf_vnds_start[current_node] >= __llvm_prf_vnds_end ||
>+	    &__llvm_prf_vnds_start[current_node + 1] > __llvm_prf_vnds_end)
>+		return NULL;
>+
>+	return &__llvm_prf_vnds_start[current_node];
>+}
>+
>+/*
>+ * Counts the number of times a target value is seen.
>+ *
>+ * Records the target value for the CounterIndex if not seen before. Otherwise,
>+ * increments the counter associated w/ the target value.
>+ */
>+void __llvm_profile_instrument_target(u64 target_value, void *data, u32 index)
>+{
>+	struct llvm_prf_data *p = (struct llvm_prf_data *)data;
>+	struct llvm_prf_value_node **counters;
>+	struct llvm_prf_value_node *curr;
>+	struct llvm_prf_value_node *min = NULL;
>+	struct llvm_prf_value_node *prev = NULL;
>+	u64 min_count = U64_MAX;
>+	u8 values = 0;
>+	unsigned long flags;
>+
>+	if (!p || !p->values)
>+		return;
>+
>+	counters = (struct llvm_prf_value_node **)p->values;
>+	curr = counters[index];
>+
>+	while (curr) {
>+		if (target_value == curr->value) {
>+			curr->count++;
>+			return;
>+		}
>+
>+		if (curr->count < min_count) {
>+			min_count = curr->count;
>+			min = curr;
>+		}
>+
>+		prev = curr;
>+		curr = curr->next;
>+		values++;
>+	}
>+
>+	if (values >= LLVM_PRF_MAX_NUM_VALS_PER_SITE) {
>+		if (!min->count || !(--min->count)) {
>+			curr = min;
>+			curr->value = target_value;
>+			curr->count++;
>+		}
>+		return;
>+	}
>+
>+	/* Lock when updating the value node structure. */
>+	flags = prf_lock();
>+
>+	curr = allocate_node(p, index, target_value);
>+	if (!curr)
>+		goto out;
>+
>+	curr->value = target_value;
>+	curr->count++;
>+
>+	if (!counters[index])
>+		counters[index] = curr;
>+	else if (prev && !prev->next)
>+		prev->next = curr;
>+
>+out:
>+	prf_unlock(flags);
>+}
>+EXPORT_SYMBOL(__llvm_profile_instrument_target);
>+
>+/* Counts the number of times a range of targets values are seen. */
>+void __llvm_profile_instrument_range(u64 target_value, void *data,
>+				     u32 index, s64 precise_start,
>+				     s64 precise_last, s64 large_value)
>+{
>+	if (large_value != S64_MIN && (s64)target_value >= large_value)
>+		target_value = large_value;
>+	else if ((s64)target_value < precise_start ||
>+		 (s64)target_value > precise_last)
>+		target_value = precise_last + 1;
>+
>+	__llvm_profile_instrument_target(target_value, data, index);
>+}
>+EXPORT_SYMBOL(__llvm_profile_instrument_range);
>diff --git a/kernel/pgo/pgo.h b/kernel/pgo/pgo.h
>new file mode 100644
>index 0000000000000..df0aa278f28bd
>--- /dev/null
>+++ b/kernel/pgo/pgo.h
>@@ -0,0 +1,206 @@
>+/* SPDX-License-Identifier: GPL-2.0 */
>+/*
>+ * Copyright (C) 2019 Google, Inc.
>+ *
>+ * Author:
>+ *	Sami Tolvanen <samitolvanen@google.com>
>+ *
>+ * This software is licensed under the terms of the GNU General Public
>+ * License version 2, as published by the Free Software Foundation, and
>+ * may be copied, distributed, and modified under those terms.
>+ *
>+ * This program is distributed in the hope that it will be useful,
>+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
>+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>+ * GNU General Public License for more details.
>+ *
>+ */
>+
>+#ifndef _PGO_H
>+#define _PGO_H
>+
>+/*
>+ * Note: These internal LLVM definitions must match the compiler version.
>+ * See llvm/include/llvm/ProfileData/InstrProfData.inc in LLVM's source code.
>+ */
>+
>+#ifdef CONFIG_64BIT
>+	#define LLVM_PRF_MAGIC		\
>+		((u64)255 << 56 |	\
>+		 (u64)'l' << 48 |	\
>+		 (u64)'p' << 40 |	\
>+		 (u64)'r' << 32 |	\
>+		 (u64)'o' << 24 |	\
>+		 (u64)'f' << 16 |	\
>+		 (u64)'r' << 8  |	\
>+		 (u64)129)
>+#else
>+	#define LLVM_PRF_MAGIC		\
>+		((u64)255 << 56 |	\
>+		 (u64)'l' << 48 |	\
>+		 (u64)'p' << 40 |	\
>+		 (u64)'r' << 32 |	\
>+		 (u64)'o' << 24 |	\
>+		 (u64)'f' << 16 |	\
>+		 (u64)'R' << 8  |	\
>+		 (u64)129)
>+#endif
>+
>+#define LLVM_PRF_VERSION		5
>+#define LLVM_PRF_DATA_ALIGN		8
>+#define LLVM_PRF_IPVK_FIRST		0
>+#define LLVM_PRF_IPVK_LAST		1
>+#define LLVM_PRF_MAX_NUM_VALS_PER_SITE	16
>+
>+#define LLVM_PRF_VARIANT_MASK_IR	(0x1ull << 56)
>+#define LLVM_PRF_VARIANT_MASK_CSIR	(0x1ull << 57)
>+
>+/**
>+ * struct llvm_prf_header - represents the raw profile header data structure.
>+ * @magic: the magic token for the file format.
>+ * @version: the version of the file format.
>+ * @data_size: the number of entries in the profile data section.
>+ * @padding_bytes_before_counters: the number of padding bytes before the
>+ *   counters.
>+ * @counters_size: the size in bytes of the LLVM profile section containing the
>+ *   counters.
>+ * @padding_bytes_after_counters: the number of padding bytes after the
>+ *   counters.
>+ * @names_size: the size in bytes of the LLVM profile section containing the
>+ *   counters' names.
>+ * @counters_delta: the beginning of the LLMV profile counters section.
>+ * @names_delta: the beginning of the LLMV profile names section.
>+ * @value_kind_last: the last profile value kind.
>+ */
>+struct llvm_prf_header {
>+	u64 magic;
>+	u64 version;
>+	u64 data_size;
>+	u64 padding_bytes_before_counters;
>+	u64 counters_size;
>+	u64 padding_bytes_after_counters;
>+	u64 names_size;
>+	u64 counters_delta;
>+	u64 names_delta;
>+	u64 value_kind_last;
>+};
>+
>+/**
>+ * struct llvm_prf_data - represents the per-function control structure.
>+ * @name_ref: the reference to the function's name.
>+ * @func_hash: the hash value of the function.
>+ * @counter_ptr: a pointer to the profile counter.
>+ * @function_ptr: a pointer to the function.
>+ * @values: the profiling values associated with this function.
>+ * @num_counters: the number of counters in the function.
>+ * @num_value_sites: the number of value profile sites.
>+ */
>+struct llvm_prf_data {
>+	const u64 name_ref;
>+	const u64 func_hash;
>+	const void *counter_ptr;
>+	const void *function_ptr;
>+	void *values;
>+	const u32 num_counters;
>+	const u16 num_value_sites[LLVM_PRF_IPVK_LAST + 1];
>+} __aligned(LLVM_PRF_DATA_ALIGN);
>+
>+/**
>+ * structure llvm_prf_value_node_data - represents the data part of the struct
>+ *   llvm_prf_value_node data structure.
>+ * @value: the value counters.
>+ * @count: the counters' count.
>+ */
>+struct llvm_prf_value_node_data {
>+	u64 value;
>+	u64 count;
>+};
>+
>+/**
>+ * struct llvm_prf_value_node - represents an internal data structure used by
>+ *   the value profiler.
>+ * @value: the value counters.
>+ * @count: the counters' count.
>+ * @next: the next value node.
>+ */
>+struct llvm_prf_value_node {
>+	u64 value;
>+	u64 count;
>+	struct llvm_prf_value_node *next;
>+};
>+
>+/**
>+ * struct llvm_prf_value_data - represents the value profiling data in indexed
>+ *   format.
>+ * @total_size: the total size in bytes including this field.
>+ * @num_value_kinds: the number of value profile kinds that has value profile
>+ *   data.
>+ */
>+struct llvm_prf_value_data {
>+	u32 total_size;
>+	u32 num_value_kinds;
>+};
>+
>+/**
>+ * struct llvm_prf_value_record - represents the on-disk layout of the value
>+ *   profile data of a particular kind for one function.
>+ * @kind: the kind of the value profile record.
>+ * @num_value_sites: the number of value profile sites.
>+ * @site_count_array: the first element of the array that stores the number
>+ *   of profiled values for each value site.
>+ */
>+struct llvm_prf_value_record {
>+	u32 kind;
>+	u32 num_value_sites;
>+	u8 site_count_array[];
>+};
>+
>+#define prf_get_value_record_header_size()		\
>+	offsetof(struct llvm_prf_value_record, site_count_array)
>+#define prf_get_value_record_site_count_size(sites)	\
>+	roundup((sites), 8)
>+#define prf_get_value_record_size(sites)		\
>+	(prf_get_value_record_header_size() +		\
>+	 prf_get_value_record_site_count_size((sites)))
>+
>+/* Data sections */
>+extern struct llvm_prf_data __llvm_prf_data_start[];
>+extern struct llvm_prf_data __llvm_prf_data_end[];
>+
>+extern u64 __llvm_prf_cnts_start[];
>+extern u64 __llvm_prf_cnts_end[];
>+
>+extern char __llvm_prf_names_start[];
>+extern char __llvm_prf_names_end[];
>+
>+extern struct llvm_prf_value_node __llvm_prf_vnds_start[];
>+extern struct llvm_prf_value_node __llvm_prf_vnds_end[];
>+
>+/* Locking for vnodes */
>+extern unsigned long prf_lock(void);
>+extern void prf_unlock(unsigned long flags);
>+
>+#define __DEFINE_PRF_SIZE(s) \
>+	static inline unsigned long prf_ ## s ## _size(void)		\
>+	{								\
>+		unsigned long start =					\
>+			(unsigned long)__llvm_prf_ ## s ## _start;	\
>+		unsigned long end =					\
>+			(unsigned long)__llvm_prf_ ## s ## _end;	\
>+		return roundup(end - start,				\
>+				sizeof(__llvm_prf_ ## s ## _start[0]));	\
>+	}								\
>+	static inline unsigned long prf_ ## s ## _count(void)		\
>+	{								\
>+		return prf_ ## s ## _size() /				\
>+			sizeof(__llvm_prf_ ## s ## _start[0]);		\
>+	}
>+
>+__DEFINE_PRF_SIZE(data);
>+__DEFINE_PRF_SIZE(cnts);
>+__DEFINE_PRF_SIZE(names);
>+__DEFINE_PRF_SIZE(vnds);
>+
>+#undef __DEFINE_PRF_SIZE
>+
>+#endif /* _PGO_H */
>diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
>index 213677a5ed33e..9b218afb5cb87 100644
>--- a/scripts/Makefile.lib
>+++ b/scripts/Makefile.lib
>@@ -143,6 +143,16 @@ _c_flags += $(if $(patsubst n%,, \
> 		$(CFLAGS_GCOV))
> endif
>
>+#
>+# Enable clang's PGO profiling flags for a file or directory depending on
>+# variables PGO_PROFILE_obj.o and PGO_PROFILE.
>+#
>+ifeq ($(CONFIG_PGO_CLANG),y)
>+_c_flags += $(if $(patsubst n%,, \
>+		$(PGO_PROFILE_$(basetarget).o)$(PGO_PROFILE)y), \
>+		$(CFLAGS_PGO_CLANG))
>+endif
>+
> #
> # Enable address sanitizer flags for kernel except some files or directories
> # we don't want to check (depends on variables KASAN_SANITIZE_obj.o, KASAN_SANITIZE)
>-- 
>2.30.0.284.gd98b1dd5eaa7-goog
>
>-- 
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Bill Wendling Jan. 11, 2021, 8:23 p.m. UTC | #7
On Mon, Jan 11, 2021 at 12:12 PM Fangrui Song <maskray@google.com> wrote:
>
> On 2021-01-11, 'Bill Wendling' via Clang Built Linux wrote:
> >From: Sami Tolvanen <samitolvanen@google.com>
> >
> >Enable the use of clang's Profile-Guided Optimization[1]. To generate a
> >profile, the kernel is instrumented with PGO counters, a representative
> >workload is run, and the raw profile data is collected from
> >/sys/kernel/debug/pgo/profraw.
> >
> >The raw profile data must be processed by clang's "llvm-profdata" tool before
> >it can be used during recompilation:
> >
> >  $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
> >  $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> >
> >Multiple raw profiles may be merged during this step.
> >
> >The data can be used either by the compiler if LTO isn't enabled:
> >
> >    ... -fprofile-use=vmlinux.profdata ...
> >
> >or by LLD if LTO is enabled:
> >
> >    ... -lto-cs-profile-file=vmlinux.profdata ...
>
> This LLD option does not exist.
> LLD does have some `--lto-*` options but the `-lto-*` form is not supported
> (it clashes with -l) https://reviews.llvm.org/D79371
>
That's strange. I've been using that option for years now. :-) Is this
a recent change?

> (There is an earlier -fprofile-instr-generate which does
> instrumentation in Clang, but the option does not have broad usage.
> It is used more for code coverage, not for optimization.
> Noticeably, it does not even implement the Kirchhoff's current law
> optimization)
>
Right. I've been told outside of this email that -fprofile-generate is
the prefered flag to use.

> -fprofile-use= is used by both regular PGO and context-sensitive PGO (CSPGO).
>
> clang -flto=thin -fprofile-use= passes -plugin-opt=cs-profile-path= to the linker.
> For regular PGO, this option is effectively a no-op (confirmed with CSPGO main developer).
>
> So I think the "or by LLD if LTO is enabled:" part should be removed.

But what if you specify the linking step explicitly? Linux doesn't
call "clang" when linking, but "ld.lld".

-bw
Fangrui Song Jan. 11, 2021, 8:31 p.m. UTC | #8
On 2021-01-11, Bill Wendling wrote:
>On Mon, Jan 11, 2021 at 12:12 PM Fangrui Song <maskray@google.com> wrote:
>>
>> On 2021-01-11, 'Bill Wendling' via Clang Built Linux wrote:
>> >From: Sami Tolvanen <samitolvanen@google.com>
>> >
>> >Enable the use of clang's Profile-Guided Optimization[1]. To generate a
>> >profile, the kernel is instrumented with PGO counters, a representative
>> >workload is run, and the raw profile data is collected from
>> >/sys/kernel/debug/pgo/profraw.
>> >
>> >The raw profile data must be processed by clang's "llvm-profdata" tool before
>> >it can be used during recompilation:
>> >
>> >  $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
>> >  $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
>> >
>> >Multiple raw profiles may be merged during this step.
>> >
>> >The data can be used either by the compiler if LTO isn't enabled:
>> >
>> >    ... -fprofile-use=vmlinux.profdata ...
>> >
>> >or by LLD if LTO is enabled:
>> >
>> >    ... -lto-cs-profile-file=vmlinux.profdata ...
>>
>> This LLD option does not exist.
>> LLD does have some `--lto-*` options but the `-lto-*` form is not supported
>> (it clashes with -l) https://reviews.llvm.org/D79371
>>
>That's strange. I've been using that option for years now. :-) Is this
>a recent change?

The more frequently used options (specifyed by the clang driver) are
-plugin-opt=... (options implemented by LLVMgold.so).
`-lto-*` is rare.

>> (There is an earlier -fprofile-instr-generate which does
>> instrumentation in Clang, but the option does not have broad usage.
>> It is used more for code coverage, not for optimization.
>> Noticeably, it does not even implement the Kirchhoff's current law
>> optimization)
>>
>Right. I've been told outside of this email that -fprofile-generate is
>the prefered flag to use.
>
>> -fprofile-use= is used by both regular PGO and context-sensitive PGO (CSPGO).
>>
>> clang -flto=thin -fprofile-use= passes -plugin-opt=cs-profile-path= to the linker.
>> For regular PGO, this option is effectively a no-op (confirmed with CSPGO main developer).
>>
>> So I think the "or by LLD if LTO is enabled:" part should be removed.
>
>But what if you specify the linking step explicitly? Linux doesn't
>call "clang" when linking, but "ld.lld".

Regular PGO+LTO does not need -plugin-opt=cs-profile-path=
CSPGO+LTO needs it.
Because -fprofile-use= may be used by both, Clang driver adds it.
CSPGO is relevant in this this patch, so the linker option does not need to be mentioned.
Nathan Chancellor Jan. 11, 2021, 9:04 p.m. UTC | #9
On Mon, Jan 11, 2021 at 12:18:21AM -0800, Bill Wendling wrote:
> From: Sami Tolvanen <samitolvanen@google.com>
> 
> Enable the use of clang's Profile-Guided Optimization[1]. To generate a
> profile, the kernel is instrumented with PGO counters, a representative
> workload is run, and the raw profile data is collected from
> /sys/kernel/debug/pgo/profraw.
> 
> The raw profile data must be processed by clang's "llvm-profdata" tool before
> it can be used during recompilation:
> 
>   $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
>   $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> 
> Multiple raw profiles may be merged during this step.
> 
> The data can be used either by the compiler if LTO isn't enabled:
> 
>     ... -fprofile-use=vmlinux.profdata ...
> 
> or by LLD if LTO is enabled:
> 
>     ... -lto-cs-profile-file=vmlinux.profdata ...
> 
> This initial submission is restricted to x86, as that's the platform we know
> works. This restriction can be lifted once other platforms have been verified
> to work with PGO.
> 
> Note that this method of profiling the kernel is clang-native and isn't
> compatible with clang's gcov support in kernel/gcov.
> 
> [1] https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> Co-developed-by: Bill Wendling <morbo@google.com>
> Signed-off-by: Bill Wendling <morbo@google.com>

I took this for a spin against x86_64_defconfig and ran into two issues:

1. https://github.com/ClangBuiltLinux/linux/issues/1252

   There is also one in drivers/gpu/drm/i915/i915_query.c. For the time
   being, I added PGO_PROFILE_... := n for those two files.

2. After doing that, I run into an undefined function error with ld.lld.

How I tested:

$ make -skj"$(nproc)" LLVM=1 defconfig

$ scripts/config -e PGO_CLANG

$ make -skj"$(nproc)" LLVM=1 olddefconfig vmlinux all
ld.lld: error: undefined symbol: __llvm_profile_instrument_memop
>>> referenced by head64.c
>>>               arch/x86/kernel/head64.o:(__early_make_pgtable)
>>> referenced by head64.c
>>>               arch/x86/kernel/head64.o:(x86_64_start_kernel)
>>> referenced by head64.c
>>>               arch/x86/kernel/head64.o:(copy_bootdata)
>>> referenced 2259 more times

Local diff:

diff --git a/drivers/char/Makefile b/drivers/char/Makefile
index ffce287ef415..4b2f238770b5 100644
--- a/drivers/char/Makefile
+++ b/drivers/char/Makefile
@@ -4,6 +4,7 @@
 #
 
 obj-y				+= mem.o random.o
+PGO_PROFILE_random.o		:= n
 obj-$(CONFIG_TTY_PRINTK)	+= ttyprintk.o
 obj-y				+= misc.o
 obj-$(CONFIG_ATARI_DSP56K)	+= dsp56k.o
diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
index e5574e506a5c..d83cacc79b1a 100644
--- a/drivers/gpu/drm/i915/Makefile
+++ b/drivers/gpu/drm/i915/Makefile
@@ -168,6 +168,7 @@ i915-y += \
 	  i915_vma.o \
 	  intel_region_lmem.o \
 	  intel_wopcm.o
+PGO_PROFILE_i915_query.o := n
 
 # general-purpose microcontroller (GuC) support
 i915-y += gt/uc/intel_uc.o \
Nick Desaulniers Jan. 11, 2021, 9:17 p.m. UTC | #10
On Mon, Jan 11, 2021 at 1:04 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> On Mon, Jan 11, 2021 at 12:18:21AM -0800, Bill Wendling wrote:
> > From: Sami Tolvanen <samitolvanen@google.com>
> >
> > Enable the use of clang's Profile-Guided Optimization[1]. To generate a
> > profile, the kernel is instrumented with PGO counters, a representative
> > workload is run, and the raw profile data is collected from
> > /sys/kernel/debug/pgo/profraw.
> >
> > The raw profile data must be processed by clang's "llvm-profdata" tool before
> > it can be used during recompilation:
> >
> >   $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
> >   $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> >
> > Multiple raw profiles may be merged during this step.
> >
> > The data can be used either by the compiler if LTO isn't enabled:
> >
> >     ... -fprofile-use=vmlinux.profdata ...
> >
> > or by LLD if LTO is enabled:
> >
> >     ... -lto-cs-profile-file=vmlinux.profdata ...
> >
> > This initial submission is restricted to x86, as that's the platform we know
> > works. This restriction can be lifted once other platforms have been verified
> > to work with PGO.
> >
> > Note that this method of profiling the kernel is clang-native and isn't
> > compatible with clang's gcov support in kernel/gcov.
> >
> > [1] https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
> >
> > Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> > Co-developed-by: Bill Wendling <morbo@google.com>
> > Signed-off-by: Bill Wendling <morbo@google.com>
>
> I took this for a spin against x86_64_defconfig and ran into two issues:
>
> 1. https://github.com/ClangBuiltLinux/linux/issues/1252

"Cannot split an edge from a CallBrInst"
Looks like that should be fixed first, then we should gate this
feature on clang-12.

>
>    There is also one in drivers/gpu/drm/i915/i915_query.c. For the time
>    being, I added PGO_PROFILE_... := n for those two files.
>
> 2. After doing that, I run into an undefined function error with ld.lld.
>
> How I tested:
>
> $ make -skj"$(nproc)" LLVM=1 defconfig
>
> $ scripts/config -e PGO_CLANG
>
> $ make -skj"$(nproc)" LLVM=1 olddefconfig vmlinux all
> ld.lld: error: undefined symbol: __llvm_profile_instrument_memop

Err...that seems like it should be implemented in
kernel/pgo/instrument.c in this patch in a v2?

> >>> referenced by head64.c
> >>>               arch/x86/kernel/head64.o:(__early_make_pgtable)
> >>> referenced by head64.c
> >>>               arch/x86/kernel/head64.o:(x86_64_start_kernel)
> >>> referenced by head64.c
> >>>               arch/x86/kernel/head64.o:(copy_bootdata)
> >>> referenced 2259 more times
>
> Local diff:
>
> diff --git a/drivers/char/Makefile b/drivers/char/Makefile
> index ffce287ef415..4b2f238770b5 100644
> --- a/drivers/char/Makefile
> +++ b/drivers/char/Makefile
> @@ -4,6 +4,7 @@
>  #
>
>  obj-y                          += mem.o random.o
> +PGO_PROFILE_random.o           := n
>  obj-$(CONFIG_TTY_PRINTK)       += ttyprintk.o
>  obj-y                          += misc.o
>  obj-$(CONFIG_ATARI_DSP56K)     += dsp56k.o
> diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
> index e5574e506a5c..d83cacc79b1a 100644
> --- a/drivers/gpu/drm/i915/Makefile
> +++ b/drivers/gpu/drm/i915/Makefile
> @@ -168,6 +168,7 @@ i915-y += \
>           i915_vma.o \
>           intel_region_lmem.o \
>           intel_wopcm.o
> +PGO_PROFILE_i915_query.o := n
>
>  # general-purpose microcontroller (GuC) support
>  i915-y += gt/uc/intel_uc.o \

I'd rather have these both sorted out before landing with PGO disabled
on these files.
Bill Wendling Jan. 11, 2021, 9:32 p.m. UTC | #11
On Mon, Jan 11, 2021 at 1:18 PM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Mon, Jan 11, 2021 at 1:04 PM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
> >
> > On Mon, Jan 11, 2021 at 12:18:21AM -0800, Bill Wendling wrote:
> > > From: Sami Tolvanen <samitolvanen@google.com>
> > >
> > > Enable the use of clang's Profile-Guided Optimization[1]. To generate a
> > > profile, the kernel is instrumented with PGO counters, a representative
> > > workload is run, and the raw profile data is collected from
> > > /sys/kernel/debug/pgo/profraw.
> > >
> > > The raw profile data must be processed by clang's "llvm-profdata" tool before
> > > it can be used during recompilation:
> > >
> > >   $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
> > >   $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> > >
> > > Multiple raw profiles may be merged during this step.
> > >
> > > The data can be used either by the compiler if LTO isn't enabled:
> > >
> > >     ... -fprofile-use=vmlinux.profdata ...
> > >
> > > or by LLD if LTO is enabled:
> > >
> > >     ... -lto-cs-profile-file=vmlinux.profdata ...
> > >
> > > This initial submission is restricted to x86, as that's the platform we know
> > > works. This restriction can be lifted once other platforms have been verified
> > > to work with PGO.
> > >
> > > Note that this method of profiling the kernel is clang-native and isn't
> > > compatible with clang's gcov support in kernel/gcov.
> > >
> > > [1] https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
> > >
> > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> > > Co-developed-by: Bill Wendling <morbo@google.com>
> > > Signed-off-by: Bill Wendling <morbo@google.com>
> >
> > I took this for a spin against x86_64_defconfig and ran into two issues:
> >
> > 1. https://github.com/ClangBuiltLinux/linux/issues/1252
>
> "Cannot split an edge from a CallBrInst"
> Looks like that should be fixed first, then we should gate this
> feature on clang-12.
>
Weird. I'll investigate.

> >
> >    There is also one in drivers/gpu/drm/i915/i915_query.c. For the time
> >    being, I added PGO_PROFILE_... := n for those two files.
> >
> > 2. After doing that, I run into an undefined function error with ld.lld.
> >
> > How I tested:
> >
> > $ make -skj"$(nproc)" LLVM=1 defconfig
> >
> > $ scripts/config -e PGO_CLANG
> >
> > $ make -skj"$(nproc)" LLVM=1 olddefconfig vmlinux all
> > ld.lld: error: undefined symbol: __llvm_profile_instrument_memop
>
> Err...that seems like it should be implemented in
> kernel/pgo/instrument.c in this patch in a v2?
>
Yes. I'll submit a new V2 with this and other feedback integrated.

> > >>> referenced by head64.c
> > >>>               arch/x86/kernel/head64.o:(__early_make_pgtable)
> > >>> referenced by head64.c
> > >>>               arch/x86/kernel/head64.o:(x86_64_start_kernel)
> > >>> referenced by head64.c
> > >>>               arch/x86/kernel/head64.o:(copy_bootdata)
> > >>> referenced 2259 more times
> >
> > Local diff:
> >
> > diff --git a/drivers/char/Makefile b/drivers/char/Makefile
> > index ffce287ef415..4b2f238770b5 100644
> > --- a/drivers/char/Makefile
> > +++ b/drivers/char/Makefile
> > @@ -4,6 +4,7 @@
> >  #
> >
> >  obj-y                          += mem.o random.o
> > +PGO_PROFILE_random.o           := n
> >  obj-$(CONFIG_TTY_PRINTK)       += ttyprintk.o
> >  obj-y                          += misc.o
> >  obj-$(CONFIG_ATARI_DSP56K)     += dsp56k.o
> > diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
> > index e5574e506a5c..d83cacc79b1a 100644
> > --- a/drivers/gpu/drm/i915/Makefile
> > +++ b/drivers/gpu/drm/i915/Makefile
> > @@ -168,6 +168,7 @@ i915-y += \
> >           i915_vma.o \
> >           intel_region_lmem.o \
> >           intel_wopcm.o
> > +PGO_PROFILE_i915_query.o := n
> >
> >  # general-purpose microcontroller (GuC) support
> >  i915-y += gt/uc/intel_uc.o \
>
> I'd rather have these both sorted out before landing with PGO disabled
> on these files.
>
Agreed.

-bw
Bill Wendling Jan. 12, 2021, 12:37 a.m. UTC | #12
On Mon, Jan 11, 2021 at 12:31 PM Fangrui Song <maskray@google.com> wrote:
> On 2021-01-11, Bill Wendling wrote:
> >On Mon, Jan 11, 2021 at 12:12 PM Fangrui Song <maskray@google.com> wrote:
> >>
> >> On 2021-01-11, 'Bill Wendling' via Clang Built Linux wrote:
> >> >From: Sami Tolvanen <samitolvanen@google.com>
> >> >
> >> >Enable the use of clang's Profile-Guided Optimization[1]. To generate a
> >> >profile, the kernel is instrumented with PGO counters, a representative
> >> >workload is run, and the raw profile data is collected from
> >> >/sys/kernel/debug/pgo/profraw.
> >> >
> >> >The raw profile data must be processed by clang's "llvm-profdata" tool before
> >> >it can be used during recompilation:
> >> >
> >> >  $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
> >> >  $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> >> >
> >> >Multiple raw profiles may be merged during this step.
> >> >
> >> >The data can be used either by the compiler if LTO isn't enabled:
> >> >
> >> >    ... -fprofile-use=vmlinux.profdata ...
> >> >
> >> >or by LLD if LTO is enabled:
> >> >
> >> >    ... -lto-cs-profile-file=vmlinux.profdata ...
> >>
> >> This LLD option does not exist.
> >> LLD does have some `--lto-*` options but the `-lto-*` form is not supported
> >> (it clashes with -l) https://reviews.llvm.org/D79371
> >>
> >That's strange. I've been using that option for years now. :-) Is this
> >a recent change?
>
> The more frequently used options (specifyed by the clang driver) are
> -plugin-opt=... (options implemented by LLVMgold.so).
> `-lto-*` is rare.
>
> >> (There is an earlier -fprofile-instr-generate which does
> >> instrumentation in Clang, but the option does not have broad usage.
> >> It is used more for code coverage, not for optimization.
> >> Noticeably, it does not even implement the Kirchhoff's current law
> >> optimization)
> >>
> >Right. I've been told outside of this email that -fprofile-generate is
> >the prefered flag to use.
> >
> >> -fprofile-use= is used by both regular PGO and context-sensitive PGO (CSPGO).
> >>
> >> clang -flto=thin -fprofile-use= passes -plugin-opt=cs-profile-path= to the linker.
> >> For regular PGO, this option is effectively a no-op (confirmed with CSPGO main developer).
> >>
> >> So I think the "or by LLD if LTO is enabled:" part should be removed.
> >
> >But what if you specify the linking step explicitly? Linux doesn't
> >call "clang" when linking, but "ld.lld".
>
> Regular PGO+LTO does not need -plugin-opt=cs-profile-path=
> CSPGO+LTO needs it.
> Because -fprofile-use= may be used by both, Clang driver adds it.
> CSPGO is relevant in this this patch, so the linker option does not need to be mentioned.

I'm still a bit confused. Are you saying that when clang uses
`-flto=thin -fprofile-use=foo` that the profile file "foo" is embedded
into the bitcode file so that when the linker's run it'll be used?

This is the workflow:

clang ... -fprofile-use=vmlinux.profdata ... -c -o foo.o foo.c
clang ... -fprofile-use=vmlinux.profdata ... -c -o bar.o bar.c
ld.lld ... <output file> foo.o bar.o

Are you saying that we don't need to have
"-plugin-opt=cs-profile-path=vmlinux.profdata" on the "ld.lld ..."
line?

-bw
Fangrui Song Jan. 12, 2021, 12:44 a.m. UTC | #13
On Mon, Jan 11, 2021 at 4:38 PM Bill Wendling <morbo@google.com> wrote:
>
> On Mon, Jan 11, 2021 at 12:31 PM Fangrui Song <maskray@google.com> wrote:
> > On 2021-01-11, Bill Wendling wrote:
> > >On Mon, Jan 11, 2021 at 12:12 PM Fangrui Song <maskray@google.com> wrote:
> > >>
> > >> On 2021-01-11, 'Bill Wendling' via Clang Built Linux wrote:
> > >> >From: Sami Tolvanen <samitolvanen@google.com>
> > >> >
> > >> >Enable the use of clang's Profile-Guided Optimization[1]. To generate a
> > >> >profile, the kernel is instrumented with PGO counters, a representative
> > >> >workload is run, and the raw profile data is collected from
> > >> >/sys/kernel/debug/pgo/profraw.
> > >> >
> > >> >The raw profile data must be processed by clang's "llvm-profdata" tool before
> > >> >it can be used during recompilation:
> > >> >
> > >> >  $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
> > >> >  $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> > >> >
> > >> >Multiple raw profiles may be merged during this step.
> > >> >
> > >> >The data can be used either by the compiler if LTO isn't enabled:
> > >> >
> > >> >    ... -fprofile-use=vmlinux.profdata ...
> > >> >
> > >> >or by LLD if LTO is enabled:
> > >> >
> > >> >    ... -lto-cs-profile-file=vmlinux.profdata ...
> > >>
> > >> This LLD option does not exist.
> > >> LLD does have some `--lto-*` options but the `-lto-*` form is not supported
> > >> (it clashes with -l) https://reviews.llvm.org/D79371
> > >>
> > >That's strange. I've been using that option for years now. :-) Is this
> > >a recent change?
> >
> > The more frequently used options (specifyed by the clang driver) are
> > -plugin-opt=... (options implemented by LLVMgold.so).
> > `-lto-*` is rare.
> >
> > >> (There is an earlier -fprofile-instr-generate which does
> > >> instrumentation in Clang, but the option does not have broad usage.
> > >> It is used more for code coverage, not for optimization.
> > >> Noticeably, it does not even implement the Kirchhoff's current law
> > >> optimization)
> > >>
> > >Right. I've been told outside of this email that -fprofile-generate is
> > >the prefered flag to use.
> > >
> > >> -fprofile-use= is used by both regular PGO and context-sensitive PGO (CSPGO).
> > >>
> > >> clang -flto=thin -fprofile-use= passes -plugin-opt=cs-profile-path= to the linker.
> > >> For regular PGO, this option is effectively a no-op (confirmed with CSPGO main developer).
> > >>
> > >> So I think the "or by LLD if LTO is enabled:" part should be removed.
> > >
> > >But what if you specify the linking step explicitly? Linux doesn't
> > >call "clang" when linking, but "ld.lld".
> >
> > Regular PGO+LTO does not need -plugin-opt=cs-profile-path=
> > CSPGO+LTO needs it.
> > Because -fprofile-use= may be used by both, Clang driver adds it.
> > CSPGO is relevant in this this patch, so the linker option does not need to be mentioned.
>
> I'm still a bit confused. Are you saying that when clang uses
> `-flto=thin -fprofile-use=foo` that the profile file "foo" is embedded
> into the bitcode file so that when the linker's run it'll be used?
>
> This is the workflow:
>
> clang ... -fprofile-use=vmlinux.profdata ... -c -o foo.o foo.c
> clang ... -fprofile-use=vmlinux.profdata ... -c -o bar.o bar.c
> ld.lld ... <output file> foo.o bar.o
>
> Are you saying that we don't need to have
> "-plugin-opt=cs-profile-path=vmlinux.profdata" on the "ld.lld ..."
> line?
>
> -bw

The backend compile step -flto=thin -fprofile-use=foo has all the information.

-plugin-opt=cs-profile-path=vmlinux.profdata is not needed for regular PGO.
Sedat Dilek Jan. 21, 2021, 2:21 a.m. UTC | #14
Hi,

When I looked through the code I wondered why we do not add a
"CONFIG_PGO_CLANG_PROFDATA" which can be helpful when doing the PGO
rebuild with a vmlinux.profdata.

This introduces a "PGO_PROFDATA" to turn on/off to pass
"-fprofile-use=vmlinux.profdata" (see CFLAGS_PGO_CLANG_PROFDATA in
top-level Makefile).

If we turn off via "PGO_PROFILE := n" in several Makefiles - we should
do the same and add "PGO_PROFDATA := n" to the same Makefiles?

Please see the attached diff.

Regards,
- Sedat -
Nick Desaulniers Jan. 22, 2021, 1:34 a.m. UTC | #15
On Wed, Jan 20, 2021 at 6:21 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> Hi,
>
> When I looked through the code I wondered why we do not add a
> "CONFIG_PGO_CLANG_PROFDATA" which can be helpful when doing the PGO
> rebuild with a vmlinux.profdata.
>
> This introduces a "PGO_PROFDATA" to turn on/off to pass
> "-fprofile-use=vmlinux.profdata" (see CFLAGS_PGO_CLANG_PROFDATA in
> top-level Makefile).
>
> If we turn off via "PGO_PROFILE := n" in several Makefiles - we should
> do the same and add "PGO_PROFDATA := n" to the same Makefiles?
>
> Please see the attached diff.

This is a good idea; something that I brought up in initial code
review (on github).  Would it be ok with you to land the core first,
then follow up with this suggestion?

Also, AutoFDO production builds are so incredibly similar to PGO
builds that I could see a possible path forward:
1. land PGO upstream
2. adds docs for AutoFDO
3. consider a config for hardcoding the location of the profiling data
so that we don't need to specify it at the command line invocation of
make.
Sedat Dilek Jan. 22, 2021, 1:43 a.m. UTC | #16
On Fri, Jan 22, 2021 at 2:34 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Wed, Jan 20, 2021 at 6:21 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
> >
> > Hi,
> >
> > When I looked through the code I wondered why we do not add a
> > "CONFIG_PGO_CLANG_PROFDATA" which can be helpful when doing the PGO
> > rebuild with a vmlinux.profdata.
> >
> > This introduces a "PGO_PROFDATA" to turn on/off to pass
> > "-fprofile-use=vmlinux.profdata" (see CFLAGS_PGO_CLANG_PROFDATA in
> > top-level Makefile).
> >
> > If we turn off via "PGO_PROFILE := n" in several Makefiles - we should
> > do the same and add "PGO_PROFDATA := n" to the same Makefiles?
> >
> > Please see the attached diff.
>
> This is a good idea; something that I brought up in initial code
> review (on github).  Would it be ok with you to land the core first,
> then follow up with this suggestion?
>
> Also, AutoFDO production builds are so incredibly similar to PGO
> builds that I could see a possible path forward:
> 1. land PGO upstream
> 2. adds docs for AutoFDO
> 3. consider a config for hardcoding the location of the profiling data
> so that we don't need to specify it at the command line invocation of
> make.
>

I made a v3 - with some small nits.
The idea was to do the "PGO-rebuild" handling a bit easier.

But as you say that can wait.

Some personal notes:

I will be very happy when people verify/confirm what's going on with
PGO-rebuild + LLVM_IAS=1.
As said GNU/AS and PGO-rebuild is fine.
( This seems to be independent of clang-12 or clang-11. )
( This seems to be independent of DWARF v4 or v5 enabled. )

The benefit here I saw was a reduction in build-time of 00:30 seen
from a total 04:30 when using a PGO-rebuilt Linux-kernel.
Approx. 10%?

This is not much compared to a ThinLTO + PGO optimized LLVM toolchain
whcih saved here 40% of build-time.

- Sedat -
diff mbox series

Patch

diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst
index f7809c7b1ba9e..8d6418e858062 100644
--- a/Documentation/dev-tools/index.rst
+++ b/Documentation/dev-tools/index.rst
@@ -26,6 +26,7 @@  whole; patches welcome!
    kgdb
    kselftest
    kunit/index
+   pgo
 
 
 .. only::  subproject and html
diff --git a/Documentation/dev-tools/pgo.rst b/Documentation/dev-tools/pgo.rst
new file mode 100644
index 0000000000000..2ed7f549b20ef
--- /dev/null
+++ b/Documentation/dev-tools/pgo.rst
@@ -0,0 +1,127 @@ 
+.. SPDX-License-Identifier: GPL-2.0
+
+===============================
+Using PGO with the Linux kernel
+===============================
+
+Clang's profiling kernel support (PGO_) enables profiling of the Linux kernel
+when building with Clang. The profiling data is exported via the ``pgo``
+debugfs directory.
+
+.. _PGO: https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
+
+
+Preparation
+===========
+
+Configure the kernel with:
+
+.. code-block:: make
+
+   CONFIG_DEBUG_FS=y
+   CONFIG_PGO_CLANG=y
+
+Note that kernels compiled with profiling flags will be significantly larger
+and run slower.
+
+Profiling data will only become accessible once debugfs has been mounted:
+
+.. code-block:: sh
+
+   mount -t debugfs none /sys/kernel/debug
+
+
+Customization
+=============
+
+You can enable or disable profiling for individual file and directories by
+adding a line similar to the following to the respective kernel Makefile:
+
+- For a single file (e.g. main.o)
+
+  .. code-block:: make
+
+     PGO_PROFILE_main.o := y
+
+- For all files in one directory
+
+  .. code-block:: make
+
+     PGO_PROFILE := y
+
+To exclude files from being profiled use
+
+  .. code-block:: make
+
+     PGO_PROFILE_main.o := n
+
+and
+
+  .. code-block:: make
+
+     PGO_PROFILE := n
+
+Only files which are linked to the main kernel image or are compiled as kernel
+modules are supported by this mechanism.
+
+
+Files
+=====
+
+The PGO kernel support creates the following files in debugfs:
+
+``/sys/kernel/debug/pgo``
+	Parent directory for all PGO-related files.
+
+``/sys/kernel/debug/pgo/reset``
+	Global reset file: resets all coverage data to zero when written to.
+
+``/sys/kernel/debug/profraw``
+	The raw PGO data that must be processed with ``llvm_profdata``.
+
+
+Workflow
+========
+
+The PGO kernel can be run on the host or test machines. The data though should
+be analyzed with Clang's tools from the same Clang version as the kernel was
+compiled. Clang's tolerant of version skew, but it's easier to use the same
+Clang version.
+
+The profiling data is useful for optimizing the kernel, analyzing coverage,
+etc. Clang offers tools to perform these tasks.
+
+Here is an example workflow for profiling an instrumented kernel with PGO and
+using the result to optimize the kernel:
+
+1) Install the kernel on the TEST machine.
+
+2) Reset the data counters right before running the load tests
+
+   .. code-block:: sh
+
+      echo 1 > /sys/kernel/debug/pgo/reset
+
+3) Run the load tests.
+
+4) Collect the raw profile data
+
+   .. code-block:: sh
+
+      cp -a /sys/kernel/debug/pgo/profraw /tmp/vmlinux.profraw
+
+5) (Optional) Download the raw profile data to the HOST machine.
+
+6) Process the raw profile data
+
+   .. code-block:: sh
+
+      llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
+
+   Note that multiple raw profile data files can be merged during this step.
+
+7) Rebuild the kernel using the profile data (PGO disabled)
+
+   .. code-block:: sh
+
+      make ... KCLAGS=-fprofile-use=vmlinux.profdata
diff --git a/MAINTAINERS b/MAINTAINERS
index 6390491b07e51..7a98bdaab9861 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -13955,6 +13955,15 @@  S:	Maintained
 F:	include/linux/personality.h
 F:	include/uapi/linux/personality.h
 
+PGO BASED KERNEL PROFILING
+M:	Sami Tolvanen <samitolvanen@google.com>
+M:	Bill Wendling <wcw@google.com>
+R:	Nathan Chancellor <natechancellor@gmail.com>
+R:	Nick Desaulniers <ndesaulniers@google.com>
+S:	Supported
+F:	Documentation/dev-tools/pgo.rst
+F:	kernel/pgo
+
 PHOENIX RC FLIGHT CONTROLLER ADAPTER
 M:	Marcus Folkesson <marcus.folkesson@gmail.com>
 L:	linux-input@vger.kernel.org
diff --git a/Makefile b/Makefile
index 8b2c3f88ee5ea..4f42957c78134 100644
--- a/Makefile
+++ b/Makefile
@@ -659,6 +659,9 @@  endif # KBUILD_EXTMOD
 # Defaults to vmlinux, but the arch makefile usually adds further targets
 all: vmlinux
 
+CFLAGS_PGO_CLANG := -fprofile-generate
+export CFLAGS_PGO_CLANG
+
 CFLAGS_GCOV	:= -fprofile-arcs -ftest-coverage \
 	$(call cc-option,-fno-tree-loop-im) \
 	$(call cc-disable-warning,maybe-uninitialized,)
diff --git a/arch/Kconfig b/arch/Kconfig
index 78c6f05b10f91..a7a6ab7d204dc 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1106,6 +1106,7 @@  config ARCH_SUPPORTS_DEBUG_PAGEALLOC
 	bool
 
 source "kernel/gcov/Kconfig"
+source "kernel/pgo/Kconfig"
 
 source "scripts/gcc-plugins/Kconfig"
 
diff --git a/arch/arm/boot/bootp/Makefile b/arch/arm/boot/bootp/Makefile
index 981a8d03f064c..523bd58df0a4b 100644
--- a/arch/arm/boot/bootp/Makefile
+++ b/arch/arm/boot/bootp/Makefile
@@ -7,6 +7,7 @@ 
 #
 
 GCOV_PROFILE	:= n
+PGO_PROFILE	:= n
 
 LDFLAGS_bootp	:= --no-undefined -X \
 		 --defsym initrd_phys=$(INITRD_PHYS) \
diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
index fb521efcc6c20..5fd0fd85fc0e5 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -24,6 +24,7 @@  OBJS		+= hyp-stub.o
 endif
 
 GCOV_PROFILE		:= n
+PGO_PROFILE		:= n
 KASAN_SANITIZE		:= n
 
 # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
diff --git a/arch/arm/vdso/Makefile b/arch/arm/vdso/Makefile
index b558bee0e1f6b..11f6ce4b48b56 100644
--- a/arch/arm/vdso/Makefile
+++ b/arch/arm/vdso/Makefile
@@ -36,8 +36,9 @@  else
 CFLAGS_vgettimeofday.o = -O2 -include $(c-gettimeofday-y)
 endif
 
-# Disable gcov profiling for VDSO code
+# Disable gcov and PGO profiling for VDSO code
 GCOV_PROFILE := n
+PGO_PROFILE := n
 
 # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
 KCOV_INSTRUMENT := n
diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
index cd9c3fa25902f..d48fc0df07020 100644
--- a/arch/arm64/kernel/vdso/Makefile
+++ b/arch/arm64/kernel/vdso/Makefile
@@ -41,8 +41,9 @@  ifneq ($(c-gettimeofday-y),)
   CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)
 endif
 
-# Disable gcov profiling for VDSO code
+# Disable gcov and PGO profiling for VDSO code
 GCOV_PROFILE := n
+PGO_PROFILE := n
 
 obj-y += vdso.o
 targets += vdso.lds
diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
index 1f1e351c5fe2b..ad128ecdbfbdf 100644
--- a/arch/arm64/kvm/hyp/nvhe/Makefile
+++ b/arch/arm64/kvm/hyp/nvhe/Makefile
@@ -60,6 +60,7 @@  KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS), $(KBUILD_CFLAG
 # compiler instrumentation that inserts callbacks or checks into the code may
 # cause crashes. Just disable it.
 GCOV_PROFILE	:= n
+PGO_PROFILE	:= n
 KASAN_SANITIZE	:= n
 UBSAN_SANITIZE	:= n
 KCOV_INSTRUMENT	:= n
diff --git a/arch/mips/boot/compressed/Makefile b/arch/mips/boot/compressed/Makefile
index 47cd9dc7454af..0855ea12f2c7f 100644
--- a/arch/mips/boot/compressed/Makefile
+++ b/arch/mips/boot/compressed/Makefile
@@ -37,6 +37,7 @@  KBUILD_AFLAGS := $(KBUILD_AFLAGS) -D__ASSEMBLY__ \
 # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
 KCOV_INSTRUMENT		:= n
 GCOV_PROFILE := n
+PGO_PROFILE := n
 
 # decompressor objects (linked with vmlinuz)
 vmlinuzobjs-y := $(obj)/head.o $(obj)/decompress.o $(obj)/string.o
diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
index 5810cc12bc1d9..d7eb64de35eae 100644
--- a/arch/mips/vdso/Makefile
+++ b/arch/mips/vdso/Makefile
@@ -66,6 +66,7 @@  ldflags-y := -Bsymbolic --no-undefined -soname=linux-vdso.so.1 \
 CFLAGS_REMOVE_vdso.o = -pg
 
 GCOV_PROFILE := n
+PGO_PROFILE := n
 UBSAN_SANITIZE := n
 KCOV_INSTRUMENT := n
 
diff --git a/arch/nds32/kernel/vdso/Makefile b/arch/nds32/kernel/vdso/Makefile
index 55df25ef00578..f2b53ee2124b7 100644
--- a/arch/nds32/kernel/vdso/Makefile
+++ b/arch/nds32/kernel/vdso/Makefile
@@ -15,9 +15,9 @@  obj-vdso := $(addprefix $(obj)/, $(obj-vdso))
 ccflags-y := -shared -fno-common -fno-builtin -nostdlib -fPIC -Wl,-shared -g \
 	-Wl,-soname=linux-vdso.so.1 -Wl,--hash-style=sysv
 
-# Disable gcov profiling for VDSO code
+# Disable gcov and PGO profiling for VDSO code
 GCOV_PROFILE := n
-
+PGO_PROFILE := n
 
 obj-y += vdso.o
 targets += vdso.lds
diff --git a/arch/parisc/boot/compressed/Makefile b/arch/parisc/boot/compressed/Makefile
index dff4536875305..5cf93a67f7da7 100644
--- a/arch/parisc/boot/compressed/Makefile
+++ b/arch/parisc/boot/compressed/Makefile
@@ -7,6 +7,7 @@ 
 
 KCOV_INSTRUMENT := n
 GCOV_PROFILE := n
+PGO_PROFILE := n
 UBSAN_SANITIZE := n
 
 targets := vmlinux.lds vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index fe2ef598e2ead..c642c046660d7 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -153,17 +153,21 @@  endif
 obj-$(CONFIG_PPC_SECURE_BOOT)	+= secure_boot.o ima_arch.o secvar-ops.o
 obj-$(CONFIG_PPC_SECVAR_SYSFS)	+= secvar-sysfs.o
 
-# Disable GCOV, KCOV & sanitizers in odd or sensitive code
+# Disable GCOV, PGO, KCOV & sanitizers in odd or sensitive code
 GCOV_PROFILE_prom_init.o := n
+PGO_PROFILE_prom_init.o := n
 KCOV_INSTRUMENT_prom_init.o := n
 UBSAN_SANITIZE_prom_init.o := n
 GCOV_PROFILE_kprobes.o := n
+PGO_PROFILE_kprobes.o := n
 KCOV_INSTRUMENT_kprobes.o := n
 UBSAN_SANITIZE_kprobes.o := n
 GCOV_PROFILE_kprobes-ftrace.o := n
+PGO_PROFILE_kprobes-ftrace.o := n
 KCOV_INSTRUMENT_kprobes-ftrace.o := n
 UBSAN_SANITIZE_kprobes-ftrace.o := n
 GCOV_PROFILE_syscall_64.o := n
+PGO_PROFILE_syscall_64.o := n
 KCOV_INSTRUMENT_syscall_64.o := n
 UBSAN_SANITIZE_syscall_64.o := n
 UBSAN_SANITIZE_vdso.o := n
diff --git a/arch/powerpc/kernel/trace/Makefile b/arch/powerpc/kernel/trace/Makefile
index 858503775c583..7d72ae7d4f8c6 100644
--- a/arch/powerpc/kernel/trace/Makefile
+++ b/arch/powerpc/kernel/trace/Makefile
@@ -23,7 +23,8 @@  obj-$(CONFIG_TRACING)			+= trace_clock.o
 obj-$(CONFIG_PPC64)			+= $(obj64-y)
 obj-$(CONFIG_PPC32)			+= $(obj32-y)
 
-# Disable GCOV, KCOV & sanitizers in odd or sensitive code
+# Disable GCOV, PGO, KCOV & sanitizers in odd or sensitive code
 GCOV_PROFILE_ftrace.o := n
+PGO_PROFILE_ftrace.o := n
 KCOV_INSTRUMENT_ftrace.o := n
 UBSAN_SANITIZE_ftrace.o := n
diff --git a/arch/powerpc/kernel/vdso32/Makefile b/arch/powerpc/kernel/vdso32/Makefile
index 9cb6f524854b9..655e159975a04 100644
--- a/arch/powerpc/kernel/vdso32/Makefile
+++ b/arch/powerpc/kernel/vdso32/Makefile
@@ -34,6 +34,7 @@  targets := $(obj-vdso32) vdso32.so.dbg
 obj-vdso32 := $(addprefix $(obj)/, $(obj-vdso32))
 
 GCOV_PROFILE := n
+PGO_PROFILE := n
 KCOV_INSTRUMENT := n
 UBSAN_SANITIZE := n
 KASAN_SANITIZE := n
diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile
index bf363ff371521..12c286f5afc16 100644
--- a/arch/powerpc/kernel/vdso64/Makefile
+++ b/arch/powerpc/kernel/vdso64/Makefile
@@ -21,6 +21,7 @@  targets := $(obj-vdso64) vdso64.so.dbg
 obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64))
 
 GCOV_PROFILE := n
+PGO_PROFILE := n
 KCOV_INSTRUMENT := n
 UBSAN_SANITIZE := n
 KASAN_SANITIZE := n
diff --git a/arch/powerpc/kexec/Makefile b/arch/powerpc/kexec/Makefile
index 4aff6846c7726..1c7f65e3cb969 100644
--- a/arch/powerpc/kexec/Makefile
+++ b/arch/powerpc/kexec/Makefile
@@ -16,7 +16,8 @@  endif
 endif
 
 
-# Disable GCOV, KCOV & sanitizers in odd or sensitive code
+# Disable GCOV, PGO, KCOV & sanitizers in odd or sensitive code
 GCOV_PROFILE_core_$(BITS).o := n
+PGO_PROFILE_core_$(BITS).o := n
 KCOV_INSTRUMENT_core_$(BITS).o := n
 UBSAN_SANITIZE_core_$(BITS).o := n
diff --git a/arch/powerpc/xmon/Makefile b/arch/powerpc/xmon/Makefile
index eb25d7554ffd1..7aff80d18b44b 100644
--- a/arch/powerpc/xmon/Makefile
+++ b/arch/powerpc/xmon/Makefile
@@ -2,6 +2,7 @@ 
 # Makefile for xmon
 
 GCOV_PROFILE := n
+PGO_PROFILE := n
 KCOV_INSTRUMENT := n
 UBSAN_SANITIZE := n
 KASAN_SANITIZE := n
diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
index 0cfd6da784f84..882340dc3c647 100644
--- a/arch/riscv/kernel/vdso/Makefile
+++ b/arch/riscv/kernel/vdso/Makefile
@@ -32,8 +32,9 @@  CPPFLAGS_vdso.lds += -P -C -U$(ARCH)
 # Disable -pg to prevent insert call site
 CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os
 
-# Disable gcov profiling for VDSO code
+# Disable gcov and PGO profiling for VDSO code
 GCOV_PROFILE := n
+PGO_PROFILE := n
 KCOV_INSTRUMENT := n
 
 # Force dependency
diff --git a/arch/s390/boot/Makefile b/arch/s390/boot/Makefile
index 41a64b8dce252..bee4a32040e79 100644
--- a/arch/s390/boot/Makefile
+++ b/arch/s390/boot/Makefile
@@ -5,6 +5,7 @@ 
 
 KCOV_INSTRUMENT := n
 GCOV_PROFILE := n
+PGO_PROFILE := n
 UBSAN_SANITIZE := n
 KASAN_SANITIZE := n
 
diff --git a/arch/s390/boot/compressed/Makefile b/arch/s390/boot/compressed/Makefile
index de18dab518bb6..c3ab883e8425a 100644
--- a/arch/s390/boot/compressed/Makefile
+++ b/arch/s390/boot/compressed/Makefile
@@ -7,6 +7,7 @@ 
 
 KCOV_INSTRUMENT := n
 GCOV_PROFILE := n
+PGO_PROFILE := n
 UBSAN_SANITIZE := n
 KASAN_SANITIZE := n
 
diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile
index dd73b7f074237..bd857aacad794 100644
--- a/arch/s390/kernel/Makefile
+++ b/arch/s390/kernel/Makefile
@@ -14,6 +14,7 @@  CFLAGS_REMOVE_early.o		= $(CC_FLAGS_FTRACE)
 endif
 
 GCOV_PROFILE_early.o		:= n
+PGO_PROFILE_early.o		:= n
 KCOV_INSTRUMENT_early.o		:= n
 UBSAN_SANITIZE_early.o		:= n
 KASAN_SANITIZE_ipl.o		:= n
diff --git a/arch/s390/kernel/vdso64/Makefile b/arch/s390/kernel/vdso64/Makefile
index a6e0fb6b91d6c..d7c43b7c1db96 100644
--- a/arch/s390/kernel/vdso64/Makefile
+++ b/arch/s390/kernel/vdso64/Makefile
@@ -35,8 +35,9 @@  obj-y += vdso64_wrapper.o
 targets += vdso64.lds
 CPPFLAGS_vdso64.lds += -P -C -U$(ARCH)
 
-# Disable gcov profiling, ubsan and kasan for VDSO code
+# Disable gcov and PGO profiling, ubsan and kasan for VDSO code
 GCOV_PROFILE := n
+PGO_PROFILE := n
 UBSAN_SANITIZE := n
 KASAN_SANITIZE := n
 
diff --git a/arch/s390/purgatory/Makefile b/arch/s390/purgatory/Makefile
index c57f8c40e9926..9aef584e98466 100644
--- a/arch/s390/purgatory/Makefile
+++ b/arch/s390/purgatory/Makefile
@@ -17,6 +17,7 @@  $(obj)/mem.o: $(srctree)/arch/s390/lib/mem.S FORCE
 
 KCOV_INSTRUMENT := n
 GCOV_PROFILE := n
+PGO_PROFILE := n
 UBSAN_SANITIZE := n
 KASAN_SANITIZE := n
 
diff --git a/arch/sh/boot/compressed/Makefile b/arch/sh/boot/compressed/Makefile
index 589d2d8a573db..ae19aeeb3964c 100644
--- a/arch/sh/boot/compressed/Makefile
+++ b/arch/sh/boot/compressed/Makefile
@@ -13,6 +13,7 @@  targets		:= vmlinux vmlinux.bin vmlinux.bin.gz \
 OBJECTS = $(obj)/head_32.o $(obj)/misc.o $(obj)/cache.o
 
 GCOV_PROFILE := n
+PGO_PROFILE := n
 
 #
 # IMAGE_OFFSET is the load offset of the compression loader
diff --git a/arch/sh/mm/Makefile b/arch/sh/mm/Makefile
index f69ddc70b1465..ea2782c631f43 100644
--- a/arch/sh/mm/Makefile
+++ b/arch/sh/mm/Makefile
@@ -43,3 +43,4 @@  obj-$(CONFIG_UNCACHED_MAPPING)	+= uncached.o
 obj-$(CONFIG_HAVE_SRAM_POOL)	+= sram.o
 
 GCOV_PROFILE_pmb.o := n
+PGO_PROFILE_pmb.o := n
diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile
index c5e1545bc5cf9..ab5f3783fe199 100644
--- a/arch/sparc/vdso/Makefile
+++ b/arch/sparc/vdso/Makefile
@@ -115,6 +115,7 @@  quiet_cmd_vdso = VDSO    $@
 
 VDSO_LDFLAGS = -shared --hash-style=both --build-id=sha1 -Bsymbolic
 GCOV_PROFILE := n
+PGO_PROFILE := n
 
 #
 # Install the unstripped copies of vdso*.so.  If our toolchain supports
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7b6dd10b162ac..a751b4f8f6645 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -95,6 +95,7 @@  config X86
 	select ARCH_SUPPORTS_DEBUG_PAGEALLOC
 	select ARCH_SUPPORTS_NUMA_BALANCING	if X86_64
 	select ARCH_SUPPORTS_KMAP_LOCAL_FORCE_MAP	if NR_CPUS <= 4096
+	select ARCH_SUPPORTS_PGO_CLANG		if X86_64
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_QUEUED_RWLOCKS
 	select ARCH_USE_QUEUED_SPINLOCKS
diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
index fe605205b4ce2..383853e32f673 100644
--- a/arch/x86/boot/Makefile
+++ b/arch/x86/boot/Makefile
@@ -71,6 +71,7 @@  KBUILD_AFLAGS	:= $(KBUILD_CFLAGS) -D__ASSEMBLY__
 KBUILD_CFLAGS	+= $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
 KBUILD_CFLAGS	+= -fno-asynchronous-unwind-tables
 GCOV_PROFILE := n
+PGO_PROFILE := n
 UBSAN_SANITIZE := n
 
 $(obj)/bzImage: asflags-y  := $(SVGA_MODE)
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index e0bc3988c3faa..ed12ab65f6065 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -54,6 +54,7 @@  CFLAGS_sev-es.o += -I$(objtree)/arch/x86/lib/
 
 KBUILD_AFLAGS  := $(KBUILD_CFLAGS) -D__ASSEMBLY__
 GCOV_PROFILE := n
+PGO_PROFILE := n
 UBSAN_SANITIZE :=n
 
 KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index 02e3e42f380bd..26e2b3af0145c 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -179,6 +179,7 @@  quiet_cmd_vdso = VDSO    $@
 VDSO_LDFLAGS = -shared --hash-style=both --build-id=sha1 \
 	$(call ld-option, --eh-frame-hdr) -Bsymbolic
 GCOV_PROFILE := n
+PGO_PROFILE := n
 
 quiet_cmd_vdso_and_check = VDSO    $@
       cmd_vdso_and_check = $(cmd_vdso); $(cmd_vdso_check)
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index efd9e9ea17f25..f6cab2316c46a 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -184,6 +184,8 @@  SECTIONS
 
 	BUG_TABLE
 
+	PGO_CLANG_DATA
+
 	ORC_UNWIND_TABLE
 
 	. = ALIGN(PAGE_SIZE);
diff --git a/arch/x86/platform/efi/Makefile b/arch/x86/platform/efi/Makefile
index 84b09c230cbd5..5f22b31446ad4 100644
--- a/arch/x86/platform/efi/Makefile
+++ b/arch/x86/platform/efi/Makefile
@@ -2,6 +2,7 @@ 
 OBJECT_FILES_NON_STANDARD_efi_thunk_$(BITS).o := y
 KASAN_SANITIZE := n
 GCOV_PROFILE := n
+PGO_PROFILE := n
 
 obj-$(CONFIG_EFI) 		+= quirks.o efi.o efi_$(BITS).o efi_stub_$(BITS).o
 obj-$(CONFIG_EFI_MIXED)		+= efi_thunk_$(BITS).o
diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index 95ea17a9d20cb..36f20e99da0bc 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -23,6 +23,7 @@  targets += purgatory.ro purgatory.chk
 
 # Sanitizer, etc. runtimes are unavailable and cannot be linked here.
 GCOV_PROFILE	:= n
+PGO_PROFILE	:= n
 KASAN_SANITIZE	:= n
 UBSAN_SANITIZE	:= n
 KCSAN_SANITIZE	:= n
diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile
index 83f1b6a56449f..21797192f958f 100644
--- a/arch/x86/realmode/rm/Makefile
+++ b/arch/x86/realmode/rm/Makefile
@@ -76,4 +76,5 @@  KBUILD_CFLAGS	:= $(REALMODE_CFLAGS) -D_SETUP -D_WAKEUP \
 KBUILD_AFLAGS	:= $(KBUILD_CFLAGS) -D__ASSEMBLY__
 KBUILD_CFLAGS	+= -fno-asynchronous-unwind-tables
 GCOV_PROFILE := n
+PGO_PROFILE := n
 UBSAN_SANITIZE := n
diff --git a/arch/x86/um/vdso/Makefile b/arch/x86/um/vdso/Makefile
index 5943387e3f357..54f5768f58530 100644
--- a/arch/x86/um/vdso/Makefile
+++ b/arch/x86/um/vdso/Makefile
@@ -64,6 +64,7 @@  quiet_cmd_vdso = VDSO    $@
 
 VDSO_LDFLAGS = -fPIC -shared -Wl,--hash-style=sysv
 GCOV_PROFILE := n
+PGO_PROFILE := n
 
 #
 # Install the unstripped copy of vdso*.so listed in $(vdso-install-y).
diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index 8a94388e38b33..2d81623b33f29 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -40,6 +40,7 @@  KBUILD_CFLAGS			:= $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
 KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))
 
 GCOV_PROFILE			:= n
+PGO_PROFILE			:= n
 # Sanitizer runtimes are unavailable and cannot be linked here.
 KASAN_SANITIZE			:= n
 KCSAN_SANITIZE			:= n
diff --git a/drivers/s390/char/Makefile b/drivers/s390/char/Makefile
index c6fdb81a068a6..bf6c5db5da1fc 100644
--- a/drivers/s390/char/Makefile
+++ b/drivers/s390/char/Makefile
@@ -9,6 +9,7 @@  CFLAGS_REMOVE_sclp_early_core.o	= $(CC_FLAGS_FTRACE)
 endif
 
 GCOV_PROFILE_sclp_early_core.o		:= n
+PGO_PROFILE_sclp_early_core.o		:= n
 KCOV_INSTRUMENT_sclp_early_core.o	:= n
 UBSAN_SANITIZE_sclp_early_core.o	:= n
 KASAN_SANITIZE_sclp_early_core.o	:= n
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index b2b3d81b1535a..3a591bb18c5fb 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -316,6 +316,49 @@ 
 #define THERMAL_TABLE(name)
 #endif
 
+#ifdef CONFIG_PGO_CLANG
+#define PGO_CLANG_DATA							\
+	__llvm_prf_data : AT(ADDR(__llvm_prf_data) - LOAD_OFFSET) {	\
+		. = ALIGN(8);						\
+		__llvm_prf_start = .;					\
+		__llvm_prf_data_start = .;				\
+		KEEP(*(__llvm_prf_data))				\
+		. = ALIGN(8);						\
+		__llvm_prf_data_end = .;				\
+	}								\
+	__llvm_prf_cnts : AT(ADDR(__llvm_prf_cnts) - LOAD_OFFSET) {	\
+		. = ALIGN(8);						\
+		__llvm_prf_cnts_start = .;				\
+		KEEP(*(__llvm_prf_cnts))				\
+		. = ALIGN(8);						\
+		__llvm_prf_cnts_end = .;				\
+	}								\
+	__llvm_prf_names : AT(ADDR(__llvm_prf_names) - LOAD_OFFSET) {	\
+		. = ALIGN(8);						\
+		__llvm_prf_names_start = .;				\
+		KEEP(*(__llvm_prf_names))				\
+		. = ALIGN(8);						\
+		__llvm_prf_names_end = .;				\
+		. = ALIGN(8);						\
+	}								\
+	__llvm_prf_vals : AT(ADDR(__llvm_prf_vals) - LOAD_OFFSET) {	\
+		__llvm_prf_vals_start = .;				\
+		KEEP(*(__llvm_prf_vals))				\
+		. = ALIGN(8);						\
+		__llvm_prf_vals_end = .;				\
+		. = ALIGN(8);						\
+	}								\
+	__llvm_prf_vnds : AT(ADDR(__llvm_prf_vnds) - LOAD_OFFSET) {	\
+		__llvm_prf_vnds_start = .;				\
+		KEEP(*(__llvm_prf_vnds))				\
+		. = ALIGN(8);						\
+		__llvm_prf_vnds_end = .;				\
+		__llvm_prf_end = .;					\
+	}
+#else
+#define PGO_CLANG_DATA
+#endif
+
 #define KERNEL_DTB()							\
 	STRUCT_ALIGN();							\
 	__dtb_start = .;						\
@@ -1125,6 +1168,7 @@ 
 		CONSTRUCTORS						\
 	}								\
 	BUG_TABLE							\
+	PGO_CLANG_DATA
 
 #define INIT_TEXT_SECTION(inittext_align)				\
 	. = ALIGN(inittext_align);					\
diff --git a/kernel/Makefile b/kernel/Makefile
index aa7368c7eabf3..0b34ca228ba46 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -111,6 +111,7 @@  obj-$(CONFIG_BPF) += bpf/
 obj-$(CONFIG_KCSAN) += kcsan/
 obj-$(CONFIG_SHADOW_CALL_STACK) += scs.o
 obj-$(CONFIG_HAVE_STATIC_CALL_INLINE) += static_call.o
+obj-$(CONFIG_PGO_CLANG) += pgo/
 
 obj-$(CONFIG_PERF_EVENTS) += events/
 
diff --git a/kernel/pgo/Kconfig b/kernel/pgo/Kconfig
new file mode 100644
index 0000000000000..318d36bb3d106
--- /dev/null
+++ b/kernel/pgo/Kconfig
@@ -0,0 +1,34 @@ 
+# SPDX-License-Identifier: GPL-2.0-only
+menu "Profile Guided Optimization (PGO) (EXPERIMENTAL)"
+
+config ARCH_SUPPORTS_PGO_CLANG
+	bool
+
+config PGO_CLANG
+	bool "Enable clang's PGO-based kernel profiling"
+	depends on DEBUG_FS
+	depends on ARCH_SUPPORTS_PGO_CLANG
+	help
+	  This option enables clang's PGO (Profile Guided Optimization) based
+	  code profiling to better optimize the kernel.
+
+	  If unsure, say N.
+
+	  Run a representative workload for your application on a kernel
+	  compiled with this option and download the raw profile file from
+	  /sys/kernel/debug/pgo/profraw. This file needs to be processed with
+	  llvm-profdata. It may be merged with other collected raw profiles.
+
+	  Copy the resulting profile file into vmlinux.profdata, and enable
+	  KCFLAGS=-fprofile-use=vmlinux.profdata to produce an optimized
+	  kernel.
+
+	  Note that a kernel compiled with profiling flags will be
+	  significatnly larger and run slower. Also be sure to exclude files
+	  from profiling which are not linked to the kernel image to prevent
+	  linker errors.
+
+	  Note that the debugfs filesystem has to be mounted to access
+	  profiling data.
+
+endmenu
diff --git a/kernel/pgo/Makefile b/kernel/pgo/Makefile
new file mode 100644
index 0000000000000..41e27cefd9a47
--- /dev/null
+++ b/kernel/pgo/Makefile
@@ -0,0 +1,5 @@ 
+# SPDX-License-Identifier: GPL-2.0
+GCOV_PROFILE	:= n
+PGO_PROFILE	:= n
+
+obj-y	+= fs.o instrument.o
diff --git a/kernel/pgo/fs.c b/kernel/pgo/fs.c
new file mode 100644
index 0000000000000..790a8df037bfc
--- /dev/null
+++ b/kernel/pgo/fs.c
@@ -0,0 +1,382 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2019 Google, Inc.
+ *
+ * Author:
+ *	Sami Tolvanen <samitolvanen@google.com>
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ */
+
+#define pr_fmt(fmt)	"pgo: " fmt
+
+#include <linux/kernel.h>
+#include <linux/debugfs.h>
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include "pgo.h"
+
+static struct dentry *directory;
+
+struct prf_private_data {
+	void *buffer;
+	unsigned long size;
+};
+
+/*
+ * Raw profile data format:
+ *
+ *	- llvm_prf_header
+ *	- __llvm_prf_data
+ *	- __llvm_prf_cnts
+ *	- __llvm_prf_names
+ *	- zero padding to 8 bytes
+ *	- for each llvm_prf_data in __llvm_prf_data:
+ *		- llvm_prf_value_data
+ *			- llvm_prf_value_record + site count array
+ *				- llvm_prf_value_node_data
+ *				...
+ *			...
+ *		...
+ */
+
+static void prf_fill_header(void **buffer)
+{
+	struct llvm_prf_header *header = *(struct llvm_prf_header **)buffer;
+
+	header->magic = LLVM_PRF_MAGIC;
+	header->version = LLVM_PRF_VARIANT_MASK_IR | LLVM_PRF_VERSION;
+	header->data_size = prf_data_count();
+	header->padding_bytes_before_counters = 0;
+	header->counters_size = prf_cnts_count();
+	header->padding_bytes_after_counters = 0;
+	header->names_size = prf_names_count();
+	header->counters_delta = (u64)__llvm_prf_cnts_start;
+	header->names_delta = (u64)__llvm_prf_names_start;
+	header->value_kind_last = LLVM_PRF_IPVK_LAST;
+
+	*buffer += sizeof(*header);
+}
+
+/*
+ * Copy the source into the buffer, incrementing the pointer into buffer in the
+ * process.
+ */
+static void prf_copy_to_buffer(void **buffer, void *src, unsigned long size)
+{
+	memcpy(*buffer, src, size);
+	*buffer += size;
+}
+
+static u32 __prf_get_value_size(struct llvm_prf_data *p, u32 *value_kinds)
+{
+	struct llvm_prf_value_node **nodes =
+		(struct llvm_prf_value_node **)p->values;
+	u32 kinds = 0;
+	u32 size = 0;
+	unsigned int kind;
+	unsigned int n;
+	unsigned int s = 0;
+
+	for (kind = 0; kind < ARRAY_SIZE(p->num_value_sites); kind++) {
+		unsigned int sites = p->num_value_sites[kind];
+
+		if (!sites)
+			continue;
+
+		/* Record + site count array */
+		size += prf_get_value_record_size(sites);
+		kinds++;
+
+		if (!nodes)
+			continue;
+
+		for (n = 0; n < sites; n++) {
+			u32 count = 0;
+			struct llvm_prf_value_node *site = nodes[s + n];
+
+			while (site && ++count <= U8_MAX)
+				site = site->next;
+
+			size += count *
+				sizeof(struct llvm_prf_value_node_data);
+		}
+
+		s += sites;
+	}
+
+	if (size)
+		size += sizeof(struct llvm_prf_value_data);
+
+	if (value_kinds)
+		*value_kinds = kinds;
+
+	return size;
+}
+
+static u32 prf_get_value_size(void)
+{
+	u32 size = 0;
+	struct llvm_prf_data *p;
+
+	for (p = __llvm_prf_data_start; p < __llvm_prf_data_end; p++)
+		size += __prf_get_value_size(p, NULL);
+
+	return size;
+}
+
+/* Serialize the profiling's value. */
+static void prf_serialize_value(struct llvm_prf_data *p, void **buffer)
+{
+	struct llvm_prf_value_data header;
+	struct llvm_prf_value_node **nodes =
+		(struct llvm_prf_value_node **)p->values;
+	unsigned int kind;
+	unsigned int n;
+	unsigned int s = 0;
+
+	header.total_size = __prf_get_value_size(p, &header.num_value_kinds);
+
+	if (!header.num_value_kinds)
+		/* Nothing to write. */
+		return;
+
+	prf_copy_to_buffer(buffer, &header, sizeof(header));
+
+	for (kind = 0; kind < ARRAY_SIZE(p->num_value_sites); kind++) {
+		struct llvm_prf_value_record *record;
+		u8 *counts;
+		unsigned int sites = p->num_value_sites[kind];
+
+		if (!sites)
+			continue;
+
+		/* Profiling value record. */
+		record = *(struct llvm_prf_value_record **)buffer;
+		*buffer += prf_get_value_record_header_size();
+
+		record->kind = kind;
+		record->num_value_sites = sites;
+
+		/* Site count array. */
+		counts = *(u8 **)buffer;
+		*buffer += prf_get_value_record_site_count_size(sites);
+
+		/*
+		 * If we don't have nodes, we can skip updating the site count
+		 * array, because the buffer is zero filled.
+		 */
+		if (!nodes)
+			continue;
+
+		for (n = 0; n < sites; n++) {
+			u32 count = 0;
+			struct llvm_prf_value_node *site = nodes[s + n];
+
+			while (site && ++count <= U8_MAX) {
+				prf_copy_to_buffer(buffer, site,
+						   sizeof(struct llvm_prf_value_node_data));
+				site = site->next;
+			}
+
+			counts[n] = (u8)count;
+		}
+
+		s += sites;
+	}
+}
+
+static void prf_serialize_values(void **buffer)
+{
+	struct llvm_prf_data *p;
+
+	for (p = __llvm_prf_data_start; p < __llvm_prf_data_end; p++)
+		prf_serialize_value(p, buffer);
+}
+
+static inline unsigned long prf_get_padding(unsigned long size)
+{
+	return 8 - (size % 8);
+}
+
+static unsigned long prf_buffer_size(void)
+{
+	return sizeof(struct llvm_prf_header) +
+			prf_data_size()	+
+			prf_cnts_size() +
+			prf_names_size() +
+			prf_get_padding(prf_names_size()) +
+			prf_get_value_size();
+}
+
+/* Serialize the profling data into a format LLVM's tools can understand. */
+static int prf_serialize(struct prf_private_data *p)
+{
+	int err = 0;
+	void *buffer;
+
+	p->size = prf_buffer_size();
+	p->buffer = vzalloc(p->size);
+
+	if (!p->buffer) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	buffer = p->buffer;
+
+	prf_fill_header(&buffer);
+	prf_copy_to_buffer(&buffer, __llvm_prf_data_start,  prf_data_size());
+	prf_copy_to_buffer(&buffer, __llvm_prf_cnts_start,  prf_cnts_size());
+	prf_copy_to_buffer(&buffer, __llvm_prf_names_start, prf_names_size());
+	buffer += prf_get_padding(prf_names_size());
+
+	prf_serialize_values(&buffer);
+
+out:
+	return err;
+}
+
+/* open() implementation for PGO. Creates a copy of the profiling data set. */
+static int prf_open(struct inode *inode, struct file *file)
+{
+	struct prf_private_data *data;
+	unsigned long flags;
+	int err;
+
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	if (!data) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	flags = prf_lock();
+
+	err = prf_serialize(data);
+	if (err) {
+		kfree(data);
+		goto out_unlock;
+	}
+
+	file->private_data = data;
+
+out_unlock:
+	prf_unlock(flags);
+out:
+	return err;
+}
+
+/* read() implementation for PGO. */
+static ssize_t prf_read(struct file *file, char __user *buf, size_t count,
+			loff_t *ppos)
+{
+	struct prf_private_data *data = file->private_data;
+
+	BUG_ON(!data);
+
+	return simple_read_from_buffer(buf, count, ppos, data->buffer,
+				       data->size);
+}
+
+/* release() implementation for PGO. Release resources allocated by open(). */
+static int prf_release(struct inode *inode, struct file *file)
+{
+	struct prf_private_data *data = file->private_data;
+
+	if (data) {
+		vfree(data->buffer);
+		kfree(data);
+	}
+
+	return 0;
+}
+
+static const struct file_operations prf_fops = {
+	.owner		= THIS_MODULE,
+	.open		= prf_open,
+	.read		= prf_read,
+	.llseek		= default_llseek,
+	.release	= prf_release
+};
+
+/* write() implementation for resetting PGO's profile data. */
+static ssize_t reset_write(struct file *file, const char __user *addr,
+			   size_t len, loff_t *pos)
+{
+	struct llvm_prf_data *data;
+
+	memset(__llvm_prf_cnts_start, 0, prf_cnts_size());
+
+	for (data = __llvm_prf_data_start; data < __llvm_prf_data_end; ++data) {
+		struct llvm_prf_value_node **vnodes;
+		u64 current_vsite_count;
+		u32 i;
+
+		if (!data->values)
+			continue;
+
+		current_vsite_count = 0;
+		vnodes = (struct llvm_prf_value_node **)data->values;
+
+		for (i = LLVM_PRF_IPVK_FIRST; i <= LLVM_PRF_IPVK_LAST; ++i)
+			current_vsite_count += data->num_value_sites[i];
+
+		for (i = 0; i < current_vsite_count; ++i) {
+			struct llvm_prf_value_node *current_vnode = vnodes[i];
+
+			while (current_vnode) {
+				current_vnode->count = 0;
+				current_vnode = current_vnode->next;
+			}
+		}
+	}
+
+	return len;
+}
+
+static const struct file_operations prf_reset_fops = {
+	.owner		= THIS_MODULE,
+	.write		= reset_write,
+	.llseek		= noop_llseek,
+};
+
+/* Create debugfs entries. */
+static int __init pgo_init(void)
+{
+	directory = debugfs_create_dir("pgo", NULL);
+	if (!directory)
+		goto err_remove;
+
+	if (!debugfs_create_file("profraw", 0600, directory, NULL,
+				 &prf_fops))
+		goto err_remove;
+
+	if (!debugfs_create_file("reset", 0200, directory, NULL,
+				 &prf_reset_fops))
+		goto err_remove;
+
+	return 0;
+
+err_remove:
+	pr_err("initialization failed\n");
+	return -EIO;
+}
+
+/* Remove debufs entries. */
+static void __exit pgo_exit(void)
+{
+	debugfs_remove_recursive(directory);
+}
+
+module_init(pgo_init);
+module_exit(pgo_exit);
diff --git a/kernel/pgo/instrument.c b/kernel/pgo/instrument.c
new file mode 100644
index 0000000000000..d96b61a1cf712
--- /dev/null
+++ b/kernel/pgo/instrument.c
@@ -0,0 +1,147 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2019 Google, Inc.
+ *
+ * Author:
+ *	Sami Tolvanen <samitolvanen@google.com>
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ */
+
+#define pr_fmt(fmt)	"pgo: " fmt
+
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/spinlock.h>
+#include <linux/types.h>
+#include "pgo.h"
+
+/* Lock guarding value node access and serialization. */
+static DEFINE_SPINLOCK(pgo_lock);
+static int current_node;
+
+unsigned long prf_lock(void)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&pgo_lock, flags);
+
+	return flags;
+}
+
+void prf_unlock(unsigned long flags)
+{
+	spin_unlock_irqrestore(&pgo_lock, flags);
+}
+
+/*
+ * Return a newly allocated profiling value node which contains the tracked
+ * value by the value profiler.
+ * Note: caller *must* hold pgo_lock.
+ */
+static struct llvm_prf_value_node *allocate_node(struct llvm_prf_data *p,
+						 u32 index, u64 value)
+{
+	if (&__llvm_prf_vnds_start[current_node + 1] >= __llvm_prf_vnds_end)
+		return NULL; /* Out of nodes */
+
+	current_node++;
+
+	/* Make sure the node is entirely within the section */
+	if (&__llvm_prf_vnds_start[current_node] >= __llvm_prf_vnds_end ||
+	    &__llvm_prf_vnds_start[current_node + 1] > __llvm_prf_vnds_end)
+		return NULL;
+
+	return &__llvm_prf_vnds_start[current_node];
+}
+
+/*
+ * Counts the number of times a target value is seen.
+ *
+ * Records the target value for the CounterIndex if not seen before. Otherwise,
+ * increments the counter associated w/ the target value.
+ */
+void __llvm_profile_instrument_target(u64 target_value, void *data, u32 index)
+{
+	struct llvm_prf_data *p = (struct llvm_prf_data *)data;
+	struct llvm_prf_value_node **counters;
+	struct llvm_prf_value_node *curr;
+	struct llvm_prf_value_node *min = NULL;
+	struct llvm_prf_value_node *prev = NULL;
+	u64 min_count = U64_MAX;
+	u8 values = 0;
+	unsigned long flags;
+
+	if (!p || !p->values)
+		return;
+
+	counters = (struct llvm_prf_value_node **)p->values;
+	curr = counters[index];
+
+	while (curr) {
+		if (target_value == curr->value) {
+			curr->count++;
+			return;
+		}
+
+		if (curr->count < min_count) {
+			min_count = curr->count;
+			min = curr;
+		}
+
+		prev = curr;
+		curr = curr->next;
+		values++;
+	}
+
+	if (values >= LLVM_PRF_MAX_NUM_VALS_PER_SITE) {
+		if (!min->count || !(--min->count)) {
+			curr = min;
+			curr->value = target_value;
+			curr->count++;
+		}
+		return;
+	}
+
+	/* Lock when updating the value node structure. */
+	flags = prf_lock();
+
+	curr = allocate_node(p, index, target_value);
+	if (!curr)
+		goto out;
+
+	curr->value = target_value;
+	curr->count++;
+
+	if (!counters[index])
+		counters[index] = curr;
+	else if (prev && !prev->next)
+		prev->next = curr;
+
+out:
+	prf_unlock(flags);
+}
+EXPORT_SYMBOL(__llvm_profile_instrument_target);
+
+/* Counts the number of times a range of targets values are seen. */
+void __llvm_profile_instrument_range(u64 target_value, void *data,
+				     u32 index, s64 precise_start,
+				     s64 precise_last, s64 large_value)
+{
+	if (large_value != S64_MIN && (s64)target_value >= large_value)
+		target_value = large_value;
+	else if ((s64)target_value < precise_start ||
+		 (s64)target_value > precise_last)
+		target_value = precise_last + 1;
+
+	__llvm_profile_instrument_target(target_value, data, index);
+}
+EXPORT_SYMBOL(__llvm_profile_instrument_range);
diff --git a/kernel/pgo/pgo.h b/kernel/pgo/pgo.h
new file mode 100644
index 0000000000000..df0aa278f28bd
--- /dev/null
+++ b/kernel/pgo/pgo.h
@@ -0,0 +1,206 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2019 Google, Inc.
+ *
+ * Author:
+ *	Sami Tolvanen <samitolvanen@google.com>
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ */
+
+#ifndef _PGO_H
+#define _PGO_H
+
+/*
+ * Note: These internal LLVM definitions must match the compiler version.
+ * See llvm/include/llvm/ProfileData/InstrProfData.inc in LLVM's source code.
+ */
+
+#ifdef CONFIG_64BIT
+	#define LLVM_PRF_MAGIC		\
+		((u64)255 << 56 |	\
+		 (u64)'l' << 48 |	\
+		 (u64)'p' << 40 |	\
+		 (u64)'r' << 32 |	\
+		 (u64)'o' << 24 |	\
+		 (u64)'f' << 16 |	\
+		 (u64)'r' << 8  |	\
+		 (u64)129)
+#else
+	#define LLVM_PRF_MAGIC		\
+		((u64)255 << 56 |	\
+		 (u64)'l' << 48 |	\
+		 (u64)'p' << 40 |	\
+		 (u64)'r' << 32 |	\
+		 (u64)'o' << 24 |	\
+		 (u64)'f' << 16 |	\
+		 (u64)'R' << 8  |	\
+		 (u64)129)
+#endif
+
+#define LLVM_PRF_VERSION		5
+#define LLVM_PRF_DATA_ALIGN		8
+#define LLVM_PRF_IPVK_FIRST		0
+#define LLVM_PRF_IPVK_LAST		1
+#define LLVM_PRF_MAX_NUM_VALS_PER_SITE	16
+
+#define LLVM_PRF_VARIANT_MASK_IR	(0x1ull << 56)
+#define LLVM_PRF_VARIANT_MASK_CSIR	(0x1ull << 57)
+
+/**
+ * struct llvm_prf_header - represents the raw profile header data structure.
+ * @magic: the magic token for the file format.
+ * @version: the version of the file format.
+ * @data_size: the number of entries in the profile data section.
+ * @padding_bytes_before_counters: the number of padding bytes before the
+ *   counters.
+ * @counters_size: the size in bytes of the LLVM profile section containing the
+ *   counters.
+ * @padding_bytes_after_counters: the number of padding bytes after the
+ *   counters.
+ * @names_size: the size in bytes of the LLVM profile section containing the
+ *   counters' names.
+ * @counters_delta: the beginning of the LLMV profile counters section.
+ * @names_delta: the beginning of the LLMV profile names section.
+ * @value_kind_last: the last profile value kind.
+ */
+struct llvm_prf_header {
+	u64 magic;
+	u64 version;
+	u64 data_size;
+	u64 padding_bytes_before_counters;
+	u64 counters_size;
+	u64 padding_bytes_after_counters;
+	u64 names_size;
+	u64 counters_delta;
+	u64 names_delta;
+	u64 value_kind_last;
+};
+
+/**
+ * struct llvm_prf_data - represents the per-function control structure.
+ * @name_ref: the reference to the function's name.
+ * @func_hash: the hash value of the function.
+ * @counter_ptr: a pointer to the profile counter.
+ * @function_ptr: a pointer to the function.
+ * @values: the profiling values associated with this function.
+ * @num_counters: the number of counters in the function.
+ * @num_value_sites: the number of value profile sites.
+ */
+struct llvm_prf_data {
+	const u64 name_ref;
+	const u64 func_hash;
+	const void *counter_ptr;
+	const void *function_ptr;
+	void *values;
+	const u32 num_counters;
+	const u16 num_value_sites[LLVM_PRF_IPVK_LAST + 1];
+} __aligned(LLVM_PRF_DATA_ALIGN);
+
+/**
+ * structure llvm_prf_value_node_data - represents the data part of the struct
+ *   llvm_prf_value_node data structure.
+ * @value: the value counters.
+ * @count: the counters' count.
+ */
+struct llvm_prf_value_node_data {
+	u64 value;
+	u64 count;
+};
+
+/**
+ * struct llvm_prf_value_node - represents an internal data structure used by
+ *   the value profiler.
+ * @value: the value counters.
+ * @count: the counters' count.
+ * @next: the next value node.
+ */
+struct llvm_prf_value_node {
+	u64 value;
+	u64 count;
+	struct llvm_prf_value_node *next;
+};
+
+/**
+ * struct llvm_prf_value_data - represents the value profiling data in indexed
+ *   format.
+ * @total_size: the total size in bytes including this field.
+ * @num_value_kinds: the number of value profile kinds that has value profile
+ *   data.
+ */
+struct llvm_prf_value_data {
+	u32 total_size;
+	u32 num_value_kinds;
+};
+
+/**
+ * struct llvm_prf_value_record - represents the on-disk layout of the value
+ *   profile data of a particular kind for one function.
+ * @kind: the kind of the value profile record.
+ * @num_value_sites: the number of value profile sites.
+ * @site_count_array: the first element of the array that stores the number
+ *   of profiled values for each value site.
+ */
+struct llvm_prf_value_record {
+	u32 kind;
+	u32 num_value_sites;
+	u8 site_count_array[];
+};
+
+#define prf_get_value_record_header_size()		\
+	offsetof(struct llvm_prf_value_record, site_count_array)
+#define prf_get_value_record_site_count_size(sites)	\
+	roundup((sites), 8)
+#define prf_get_value_record_size(sites)		\
+	(prf_get_value_record_header_size() +		\
+	 prf_get_value_record_site_count_size((sites)))
+
+/* Data sections */
+extern struct llvm_prf_data __llvm_prf_data_start[];
+extern struct llvm_prf_data __llvm_prf_data_end[];
+
+extern u64 __llvm_prf_cnts_start[];
+extern u64 __llvm_prf_cnts_end[];
+
+extern char __llvm_prf_names_start[];
+extern char __llvm_prf_names_end[];
+
+extern struct llvm_prf_value_node __llvm_prf_vnds_start[];
+extern struct llvm_prf_value_node __llvm_prf_vnds_end[];
+
+/* Locking for vnodes */
+extern unsigned long prf_lock(void);
+extern void prf_unlock(unsigned long flags);
+
+#define __DEFINE_PRF_SIZE(s) \
+	static inline unsigned long prf_ ## s ## _size(void)		\
+	{								\
+		unsigned long start =					\
+			(unsigned long)__llvm_prf_ ## s ## _start;	\
+		unsigned long end =					\
+			(unsigned long)__llvm_prf_ ## s ## _end;	\
+		return roundup(end - start,				\
+				sizeof(__llvm_prf_ ## s ## _start[0]));	\
+	}								\
+	static inline unsigned long prf_ ## s ## _count(void)		\
+	{								\
+		return prf_ ## s ## _size() /				\
+			sizeof(__llvm_prf_ ## s ## _start[0]);		\
+	}
+
+__DEFINE_PRF_SIZE(data);
+__DEFINE_PRF_SIZE(cnts);
+__DEFINE_PRF_SIZE(names);
+__DEFINE_PRF_SIZE(vnds);
+
+#undef __DEFINE_PRF_SIZE
+
+#endif /* _PGO_H */
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 213677a5ed33e..9b218afb5cb87 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -143,6 +143,16 @@  _c_flags += $(if $(patsubst n%,, \
 		$(CFLAGS_GCOV))
 endif
 
+#
+# Enable clang's PGO profiling flags for a file or directory depending on
+# variables PGO_PROFILE_obj.o and PGO_PROFILE.
+#
+ifeq ($(CONFIG_PGO_CLANG),y)
+_c_flags += $(if $(patsubst n%,, \
+		$(PGO_PROFILE_$(basetarget).o)$(PGO_PROFILE)y), \
+		$(CFLAGS_PGO_CLANG))
+endif
+
 #
 # Enable address sanitizer flags for kernel except some files or directories
 # we don't want to check (depends on variables KASAN_SANITIZE_obj.o, KASAN_SANITIZE)