diff mbox series

[v4] pgo: add clang's Profile Guided Optimization infrastructure

Message ID 20210113061958.886723-1-morbo@google.com (mailing list archive)
State New
Headers show
Series [v4] pgo: add clang's Profile Guided Optimization infrastructure | expand

Commit Message

Bill Wendling Jan. 13, 2021, 6:19 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 now be used by the compiler:

  $ make LLVM=1 KCFLAGS=-fprofile-use=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, unlike
the clang 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>
Change-Id: Ic78e69c682286d3a44c4549a0138578c98138b77
---
v2: - Added "__llvm_profile_instrument_memop" based on Nathan Chancellor's
      testing.
    - Corrected documentation, re PGO flags when using LTO, based on Fangrui
      Song's comments.
v3: - Added change log section based on Sedat Dilek's comments.
v4: - Remove non-x86 Makfile changes and se "hweight64" instead of using our
      own popcount implementation, based on Nick Desaulniers's comment.
---
 Documentation/dev-tools/index.rst     |   1 +
 Documentation/dev-tools/pgo.rst       | 127 +++++++++
 MAINTAINERS                           |   9 +
 Makefile                              |   3 +
 arch/Kconfig                          |   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 +
 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               | 185 +++++++++++++
 kernel/pgo/pgo.h                      | 206 ++++++++++++++
 scripts/Makefile.lib                  |  10 +
 23 files changed, 1019 insertions(+)
 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

Nathan Chancellor Jan. 13, 2021, 8:55 p.m. UTC | #1
Hi Bill,

On Tue, Jan 12, 2021 at 10:19:58PM -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 now be used by the compiler:
> 
>   $ make LLVM=1 KCFLAGS=-fprofile-use=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, unlike
> the clang 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>
> Change-Id: Ic78e69c682286d3a44c4549a0138578c98138b77

Small nit: This should be removed.

I applied this patch on top of v5.11-rc3, built it with LLVM 12
(f1d5cbbdee5526bc86eac0a5652b115d9bc158e5 + D94470) with Microsoft's
WSL 5.4 config [1] + CONFIG_PGO_CLANG=y, and ran it on WSL2.

$ zgrep PGO /proc/config.gz
# Profile Guided Optimization (PGO) (EXPERIMENTAL)
CONFIG_ARCH_SUPPORTS_PGO_CLANG=y
CONFIG_PGO_CLANG=y
# end of Profile Guided Optimization (PGO) (EXPERIMENTAL)

However, I see an issue with actually using the data:

$ sudo -s
# mount -t debugfs none /sys/kernel/debug
# cp -a /sys/kernel/debug/pgo/profraw vmlinux.profraw
# chown nathan:nathan vmlinux.profraw
# exit
$ tc-build/build/llvm/stage1/bin/llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
warning: vmlinux.profraw: Invalid instrumentation profile data (bad magic)
error: No profiles could be merged.

Am I holding it wrong? :) Note, this is virtualized, I do not have any
"real" x86 hardware that I can afford to test on right now.

[1]: https://github.com/microsoft/WSL2-Linux-Kernel/raw/linux-msft-wsl-5.4.y/Microsoft/config-wsl

Cheers,
Nathan
Bill Wendling Jan. 13, 2021, 9:59 p.m. UTC | #2
On Wed, Jan 13, 2021 at 12:55 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> Hi Bill,
>
> On Tue, Jan 12, 2021 at 10:19:58PM -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 now be used by the compiler:
> >
> >   $ make LLVM=1 KCFLAGS=-fprofile-use=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, unlike
> > the clang 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>
> > Change-Id: Ic78e69c682286d3a44c4549a0138578c98138b77
>
> Small nit: This should be removed.
>
Grrr....The git hook keeps adding it in there. :-(

> I applied this patch on top of v5.11-rc3, built it with LLVM 12
> (f1d5cbbdee5526bc86eac0a5652b115d9bc158e5 + D94470) with Microsoft's
> WSL 5.4 config [1] + CONFIG_PGO_CLANG=y, and ran it on WSL2.
>
> $ zgrep PGO /proc/config.gz
> # Profile Guided Optimization (PGO) (EXPERIMENTAL)
> CONFIG_ARCH_SUPPORTS_PGO_CLANG=y
> CONFIG_PGO_CLANG=y
> # end of Profile Guided Optimization (PGO) (EXPERIMENTAL)
>
> However, I see an issue with actually using the data:
>
> $ sudo -s
> # mount -t debugfs none /sys/kernel/debug
> # cp -a /sys/kernel/debug/pgo/profraw vmlinux.profraw
> # chown nathan:nathan vmlinux.profraw
> # exit
> $ tc-build/build/llvm/stage1/bin/llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> warning: vmlinux.profraw: Invalid instrumentation profile data (bad magic)
> error: No profiles could be merged.
>
> Am I holding it wrong? :) Note, this is virtualized, I do not have any
> "real" x86 hardware that I can afford to test on right now.
>
> [1]: https://github.com/microsoft/WSL2-Linux-Kernel/raw/linux-msft-wsl-5.4.y/Microsoft/config-wsl
>
Could you send me the vmlinux.profraw file? (Don't CC this list.)

-bw
Nick Desaulniers Jan. 13, 2021, 11:01 p.m. UTC | #3
On Tue, Jan 12, 2021 at 10:20 PM Bill Wendling <morbo@google.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 now be used by the compiler:
>
>   $ make LLVM=1 KCFLAGS=-fprofile-use=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, unlike
> the clang 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>
> Change-Id: Ic78e69c682286d3a44c4549a0138578c98138b77
> ---
> v2: - Added "__llvm_profile_instrument_memop" based on Nathan Chancellor's
>       testing.
>     - Corrected documentation, re PGO flags when using LTO, based on Fangrui
>       Song's comments.
> v3: - Added change log section based on Sedat Dilek's comments.
> v4: - Remove non-x86 Makfile changes and se "hweight64" instead of using our
>       own popcount implementation, based on Nick Desaulniers's comment.
> ---
>  Documentation/dev-tools/index.rst     |   1 +
>  Documentation/dev-tools/pgo.rst       | 127 +++++++++
>  MAINTAINERS                           |   9 +
>  Makefile                              |   3 +
>  arch/Kconfig                          |   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 +
>  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               | 185 +++++++++++++
>  kernel/pgo/pgo.h                      | 206 ++++++++++++++
>  scripts/Makefile.lib                  |  10 +
>  23 files changed, 1019 insertions(+)
>  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..b7f11d8405b73
> --- /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

Maybe I'm a noob, but I had to:
$ mkdir -p /sys/kernel/debug
$ mount -t debugfs none /sys/kernel/debug

first. That might trip up future travelers (like myself, I'm prone to
forget these unless they're in my shell history).

> +
> +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 LLVM=1 KCFLAGS=-fprofile-use=vmlinux.profdata ...
> diff --git a/MAINTAINERS b/MAINTAINERS
> index cc1e6a5ee6e67..1b979da316fa4 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -13954,6 +13954,15 @@ 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 9e73f82e0d863..9128bfe1ccc97 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 24862d15f3a36..f39d3991f6bfe 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -1112,6 +1112,7 @@ config ARCH_SPLIT_ARG64
>            pairs of 32-bit arguments, select this option.
>
>  source "kernel/gcov/Kconfig"
> +source "kernel/pgo/Kconfig"
>
>  source "scripts/gcc-plugins/Kconfig"
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 21f851179ff08..36305ea61dc09 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -96,6 +96,7 @@ 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/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 = .;                                \
> +       }                                                               \

So if I do a build of
$ make CC=clang
I observe the following error:
`.discard.text' referenced in section `__llvm_prf_data' of
arch/x86/kernel/setup.o: defined in discarded section `.discard.text'
of arch/x86/kernel/setup.o
`.discard.text' referenced in section `__llvm_prf_data' of
arch/x86/mm/init.o: defined in discarded section `.discard.text' of
arch/x86/mm/init.o

This can be investigated more via:
$ llvm-objdump -Dr -j __llvm_prf_data arch/x86/mm/init.o  | grep discard
                0000000000000168:  R_X86_64_64  .discard.text

So looks like a relocation is referencing something in .discard.text.

$ llvm-objdump -Dr -j .discard.text arch/x86/mm/init.o
...
0000000000000000 <__brk_reservation_fn_early_pgt_alloc__>:
       0: 48 83 05 00 00 00 00 01       addq    $1, (%rip)  # 8
<__brk_reservation_fn_early_pgt_alloc__+0x8>
                0000000000000003:  R_X86_64_PC32        __llvm_prf_cnts+0xf3
       8: c3                            retq

Looks like arch/x86/include/asm/setup.h defines the macro RESERVE_BRK
which defines a static function in the .discard.text section.  Is
there a function attribute that we can use to say "please don't
profile this one function?"

For arch/x86/kernel/setup.o it looks like the same issue with
__brk_reservation_fn_dmi_alloc__.

More specifically, this warning goes away when using LLD:
$ make CC=clang LD=ld.lld

Not sure yet why these warnings are only observed when using BFD?
Maybe LLD should also be producing this diagnostic, but is not?

Anyways, I was able to build+boot profiling mode binaries built with:
$ make LLVM=1 defconfig+PGO
$ make LLVM=1 LLVM_IAS=1 defconfig+PGO

It would be good to resolve/investigate the above error with BFD and
fix it, or make this config also depend on LLD for now. ie.
$ make CC=clang defconfig+PGO

I'm going to try rebuilding+booting with the profile data now, and
will report back.

> +       __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

probably should additionally:
  depends on CLANG_VERSION >= 120000

I'm observing the same failed assertion as Nathan trying to build
x86_64 defconfig (drivers/gpu/drm/i915/i915_query.c), that should be
fixed by:
https://reviews.llvm.org/D94470

I think that would also help prevent this config from being selectable
if not using CC=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

^ typo: significantly

> +         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. */

^ typo: profiling

> +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. */

^ typo: debugfs

> +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..6084ff0652e85
> --- /dev/null
> +++ b/kernel/pgo/instrument.c
> @@ -0,0 +1,185 @@
> +// 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/bitops.h>
> +#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);
> +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);
> +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);
> +
> +static u64 inst_prof_get_range_rep_value(u64 value)
> +{
> +       if (value <= 8)
> +               /* The first ranges are individually tracked, us it as is. */
> +               return value;
> +       else if (value >= 513)
> +               /* The last range is mapped to its lowest value. */
> +               return 513;
> +       else if (hweight64(value) == 1)
> +               /* If it's a power of two, use it as is. */
> +               return value;
> +
> +       /* Otherwise, take to the previous power of two + 1. */
> +       return (1 << (64 - __builtin_clzll(value) - 1)) + 1;
> +}
> +
> +/*
> + * The target values are partitioned into multiple ranges. The range spec is
> + * defined in compiler-rt/include/profile/InstrProfData.inc.
> + */
> +void __llvm_profile_instrument_memop(u64 target_value, void *data,
> +                                    u32 counter_index);
> +void __llvm_profile_instrument_memop(u64 target_value, void *data,
> +                                    u32 counter_index)
> +{
> +       u64 rep_value;
> +
> +       /* Map the target value to the representative value of its range. */
> +       rep_value = inst_prof_get_range_rep_value(target_value);
> +       __llvm_profile_instrument_target(rep_value, data, counter_index);
> +}
> +EXPORT_SYMBOL(__llvm_profile_instrument_memop);
> 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
>
Nick Desaulniers Jan. 14, 2021, 4:07 a.m. UTC | #4
On Wed, Jan 13, 2021 at 12:55 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> However, I see an issue with actually using the data:
>
> $ sudo -s
> # mount -t debugfs none /sys/kernel/debug
> # cp -a /sys/kernel/debug/pgo/profraw vmlinux.profraw
> # chown nathan:nathan vmlinux.profraw
> # exit
> $ tc-build/build/llvm/stage1/bin/llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> warning: vmlinux.profraw: Invalid instrumentation profile data (bad magic)
> error: No profiles could be merged.
>
> Am I holding it wrong? :) Note, this is virtualized, I do not have any
> "real" x86 hardware that I can afford to test on right now.

Same.

I think the magic calculation in this patch may differ from upstream
llvm: https://github.com/llvm/llvm-project/blob/49142991a685bd427d7e877c29c77371dfb7634c/llvm/include/llvm/ProfileData/SampleProf.h#L96-L101

vs this patch:

+ * 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
Nick Desaulniers Jan. 16, 2021, 12:01 a.m. UTC | #5
On Wed, Jan 13, 2021 at 8:07 PM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Wed, Jan 13, 2021 at 12:55 PM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
> >
> > However, I see an issue with actually using the data:
> >
> > $ sudo -s
> > # mount -t debugfs none /sys/kernel/debug
> > # cp -a /sys/kernel/debug/pgo/profraw vmlinux.profraw
> > # chown nathan:nathan vmlinux.profraw
> > # exit
> > $ tc-build/build/llvm/stage1/bin/llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> > warning: vmlinux.profraw: Invalid instrumentation profile data (bad magic)
> > error: No profiles could be merged.
> >
> > Am I holding it wrong? :) Note, this is virtualized, I do not have any
> > "real" x86 hardware that I can afford to test on right now.
>
> Same.
>
> I think the magic calculation in this patch may differ from upstream
> llvm: https://github.com/llvm/llvm-project/blob/49142991a685bd427d7e877c29c77371dfb7634c/llvm/include/llvm/ProfileData/SampleProf.h#L96-L101

Err...it looks like it was the padding calculation.  With that fixed
up, we can query the profile data to get insights on the most heavily
called functions.  Here's what my top 20 are (reset, then watch 10
minutes worth of cat videos on youtube while running `find /` and
sleeping at my desk).  Anything curious stand out to anyone?

$ llvm-profdata show -topn=20 /tmp/vmlinux.profraw
Instrumentation level: IR  entry_first = 0
Total functions: 48970
Maximum function count: 62070879
Maximum internal block count: 83221158
Top 20 functions with the largest internal block counts:
  drivers/tty/n_tty.c:n_tty_write, max count = 83221158
  rcu_read_unlock_strict, max count = 62070879
  _cond_resched, max count = 25486882
  rcu_all_qs, max count = 25451477
  drivers/cpuidle/poll_state.c:poll_idle, max count = 23618576
  _raw_spin_unlock_irqrestore, max count = 18874121
  drivers/cpuidle/governors/menu.c:menu_select, max count = 18721624
  _raw_spin_lock_irqsave, max count = 18509161
  memchr, max count = 15525452
  _raw_spin_lock, max count = 15484254
  __mod_memcg_state, max count = 14604619
  __mod_memcg_lruvec_state, max count = 14602783
  fs/ext4/hash.c:str2hashbuf_signed, max count = 14098424
  __mod_lruvec_state, max count = 12527154
  __mod_node_page_state, max count = 12525172
  native_sched_clock, max count = 8904692
  sched_clock_cpu, max count = 8895832
  sched_clock, max count = 8894627
  kernel/entry/common.c:exit_to_user_mode_prepare, max count = 8289031
  fpregs_assert_state_consistent, max count = 8287198
Nick Desaulniers Jan. 16, 2021, 12:13 a.m. UTC | #6
> On Wed, Jan 13, 2021 at 8:07 PM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > On Wed, Jan 13, 2021 at 12:55 PM Nathan Chancellor
> > <natechancellor@gmail.com> wrote:
> > >
> > > However, I see an issue with actually using the data:
> > >
> > > $ sudo -s
> > > # mount -t debugfs none /sys/kernel/debug
> > > # cp -a /sys/kernel/debug/pgo/profraw vmlinux.profraw
> > > # chown nathan:nathan vmlinux.profraw
> > > # exit
> > > $ tc-build/build/llvm/stage1/bin/llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> > > warning: vmlinux.profraw: Invalid instrumentation profile data (bad magic)
> > > error: No profiles could be merged.
> > >
> > > Am I holding it wrong? :) Note, this is virtualized, I do not have any
> > > "real" x86 hardware that I can afford to test on right now.
> >
> > Same.
> >
> > I think the magic calculation in this patch may differ from upstream
> > llvm: https://github.com/llvm/llvm-project/blob/49142991a685bd427d7e877c29c77371dfb7634c/llvm/include/llvm/ProfileData/SampleProf.h#L96-L101
> 
> Err...it looks like it was the padding calculation.  With that fixed
> up, we can query the profile data to get insights on the most heavily
> called functions.  Here's what my top 20 are (reset, then watch 10
> minutes worth of cat videos on youtube while running `find /` and
> sleeping at my desk).  Anything curious stand out to anyone?

Hello world from my personal laptop whose kernel was rebuilt with
profiling data!  Wow, I can run `find /` and watch cat videos on youtube
so fast!  Users will love this! /s

Checking the sections sizes of .text.hot. and .text.unlikely. looks
good!

> 
> $ llvm-profdata show -topn=20 /tmp/vmlinux.profraw
> Instrumentation level: IR  entry_first = 0
> Total functions: 48970
> Maximum function count: 62070879
> Maximum internal block count: 83221158
> Top 20 functions with the largest internal block counts:
>   drivers/tty/n_tty.c:n_tty_write, max count = 83221158
>   rcu_read_unlock_strict, max count = 62070879
>   _cond_resched, max count = 25486882
>   rcu_all_qs, max count = 25451477
>   drivers/cpuidle/poll_state.c:poll_idle, max count = 23618576
>   _raw_spin_unlock_irqrestore, max count = 18874121
>   drivers/cpuidle/governors/menu.c:menu_select, max count = 18721624
>   _raw_spin_lock_irqsave, max count = 18509161
>   memchr, max count = 15525452
>   _raw_spin_lock, max count = 15484254
>   __mod_memcg_state, max count = 14604619
>   __mod_memcg_lruvec_state, max count = 14602783
>   fs/ext4/hash.c:str2hashbuf_signed, max count = 14098424
>   __mod_lruvec_state, max count = 12527154
>   __mod_node_page_state, max count = 12525172
>   native_sched_clock, max count = 8904692
>   sched_clock_cpu, max count = 8895832
>   sched_clock, max count = 8894627
>   kernel/entry/common.c:exit_to_user_mode_prepare, max count = 8289031
>   fpregs_assert_state_consistent, max count = 8287198
> 
> -- 
> Thanks,
> ~Nick Desaulniers
>
Sedat Dilek Jan. 16, 2021, 4:30 a.m. UTC | #7
On Sat, Jan 16, 2021 at 1:13 AM Nick Desaulniers
<nick.desaulniers@gmail.com> wrote:
>
> > On Wed, Jan 13, 2021 at 8:07 PM Nick Desaulniers
> > <ndesaulniers@google.com> wrote:
> > >
> > > On Wed, Jan 13, 2021 at 12:55 PM Nathan Chancellor
> > > <natechancellor@gmail.com> wrote:
> > > >
> > > > However, I see an issue with actually using the data:
> > > >
> > > > $ sudo -s
> > > > # mount -t debugfs none /sys/kernel/debug
> > > > # cp -a /sys/kernel/debug/pgo/profraw vmlinux.profraw
> > > > # chown nathan:nathan vmlinux.profraw
> > > > # exit
> > > > $ tc-build/build/llvm/stage1/bin/llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> > > > warning: vmlinux.profraw: Invalid instrumentation profile data (bad magic)
> > > > error: No profiles could be merged.
> > > >
> > > > Am I holding it wrong? :) Note, this is virtualized, I do not have any
> > > > "real" x86 hardware that I can afford to test on right now.
> > >
> > > Same.
> > >
> > > I think the magic calculation in this patch may differ from upstream
> > > llvm: https://github.com/llvm/llvm-project/blob/49142991a685bd427d7e877c29c77371dfb7634c/llvm/include/llvm/ProfileData/SampleProf.h#L96-L101
> >
> > Err...it looks like it was the padding calculation.  With that fixed
> > up, we can query the profile data to get insights on the most heavily
> > called functions.  Here's what my top 20 are (reset, then watch 10
> > minutes worth of cat videos on youtube while running `find /` and
> > sleeping at my desk).  Anything curious stand out to anyone?
>
> Hello world from my personal laptop whose kernel was rebuilt with
> profiling data!  Wow, I can run `find /` and watch cat videos on youtube
> so fast!  Users will love this! /s
>
> Checking the sections sizes of .text.hot. and .text.unlikely. looks
> good!
>

I love cat videos on youtube and do find parallelly...

I must try this :-)!

Might be good to write up an instruction (README) for followers?

- Sedat -

> >
> > $ llvm-profdata show -topn=20 /tmp/vmlinux.profraw
> > Instrumentation level: IR  entry_first = 0
> > Total functions: 48970
> > Maximum function count: 62070879
> > Maximum internal block count: 83221158
> > Top 20 functions with the largest internal block counts:
> >   drivers/tty/n_tty.c:n_tty_write, max count = 83221158
> >   rcu_read_unlock_strict, max count = 62070879
> >   _cond_resched, max count = 25486882
> >   rcu_all_qs, max count = 25451477
> >   drivers/cpuidle/poll_state.c:poll_idle, max count = 23618576
> >   _raw_spin_unlock_irqrestore, max count = 18874121
> >   drivers/cpuidle/governors/menu.c:menu_select, max count = 18721624
> >   _raw_spin_lock_irqsave, max count = 18509161
> >   memchr, max count = 15525452
> >   _raw_spin_lock, max count = 15484254
> >   __mod_memcg_state, max count = 14604619
> >   __mod_memcg_lruvec_state, max count = 14602783
> >   fs/ext4/hash.c:str2hashbuf_signed, max count = 14098424
> >   __mod_lruvec_state, max count = 12527154
> >   __mod_node_page_state, max count = 12525172
> >   native_sched_clock, max count = 8904692
> >   sched_clock_cpu, max count = 8895832
> >   sched_clock, max count = 8894627
> >   kernel/entry/common.c:exit_to_user_mode_prepare, max count = 8289031
> >   fpregs_assert_state_consistent, max count = 8287198
> >
> > --
> > Thanks,
> > ~Nick Desaulniers
> >
>
> --
> 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/20210116001324.2865-1-nick.desaulniers%40gmail.com.
Sedat Dilek Jan. 16, 2021, 5:07 a.m. UTC | #8
On Sat, Jan 16, 2021 at 1:13 AM Nick Desaulniers
<nick.desaulniers@gmail.com> wrote:
>
> > On Wed, Jan 13, 2021 at 8:07 PM Nick Desaulniers
> > <ndesaulniers@google.com> wrote:
> > >
> > > On Wed, Jan 13, 2021 at 12:55 PM Nathan Chancellor
> > > <natechancellor@gmail.com> wrote:
> > > >
> > > > However, I see an issue with actually using the data:
> > > >
> > > > $ sudo -s
> > > > # mount -t debugfs none /sys/kernel/debug
> > > > # cp -a /sys/kernel/debug/pgo/profraw vmlinux.profraw
> > > > # chown nathan:nathan vmlinux.profraw
> > > > # exit
> > > > $ tc-build/build/llvm/stage1/bin/llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> > > > warning: vmlinux.profraw: Invalid instrumentation profile data (bad magic)
> > > > error: No profiles could be merged.
> > > >
> > > > Am I holding it wrong? :) Note, this is virtualized, I do not have any
> > > > "real" x86 hardware that I can afford to test on right now.
> > >
> > > Same.
> > >
> > > I think the magic calculation in this patch may differ from upstream
> > > llvm: https://github.com/llvm/llvm-project/blob/49142991a685bd427d7e877c29c77371dfb7634c/llvm/include/llvm/ProfileData/SampleProf.h#L96-L101
> >
> > Err...it looks like it was the padding calculation.  With that fixed
> > up, we can query the profile data to get insights on the most heavily
> > called functions.  Here's what my top 20 are (reset, then watch 10
> > minutes worth of cat videos on youtube while running `find /` and
> > sleeping at my desk).  Anything curious stand out to anyone?
>
> Hello world from my personal laptop whose kernel was rebuilt with
> profiling data!  Wow, I can run `find /` and watch cat videos on youtube
> so fast!  Users will love this! /s
>
> Checking the sections sizes of .text.hot. and .text.unlikely. looks
> good!
>

Is that the latest status of Bill's patch?

Or do you have me a lore link?

- Sedat -

[1] https://github.com/gwelymernans/linux/commits/gwelymernans/linux


> >
> > $ llvm-profdata show -topn=20 /tmp/vmlinux.profraw
> > Instrumentation level: IR  entry_first = 0
> > Total functions: 48970
> > Maximum function count: 62070879
> > Maximum internal block count: 83221158
> > Top 20 functions with the largest internal block counts:
> >   drivers/tty/n_tty.c:n_tty_write, max count = 83221158
> >   rcu_read_unlock_strict, max count = 62070879
> >   _cond_resched, max count = 25486882
> >   rcu_all_qs, max count = 25451477
> >   drivers/cpuidle/poll_state.c:poll_idle, max count = 23618576
> >   _raw_spin_unlock_irqrestore, max count = 18874121
> >   drivers/cpuidle/governors/menu.c:menu_select, max count = 18721624
> >   _raw_spin_lock_irqsave, max count = 18509161
> >   memchr, max count = 15525452
> >   _raw_spin_lock, max count = 15484254
> >   __mod_memcg_state, max count = 14604619
> >   __mod_memcg_lruvec_state, max count = 14602783
> >   fs/ext4/hash.c:str2hashbuf_signed, max count = 14098424
> >   __mod_lruvec_state, max count = 12527154
> >   __mod_node_page_state, max count = 12525172
> >   native_sched_clock, max count = 8904692
> >   sched_clock_cpu, max count = 8895832
> >   sched_clock, max count = 8894627
> >   kernel/entry/common.c:exit_to_user_mode_prepare, max count = 8289031
> >   fpregs_assert_state_consistent, max count = 8287198
> >
> > --
> > Thanks,
> > ~Nick Desaulniers
> >
>
> --
> 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/20210116001324.2865-1-nick.desaulniers%40gmail.com.
Sedat Dilek Jan. 16, 2021, 5:18 a.m. UTC | #9
On Sat, Jan 16, 2021 at 6:07 AM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Sat, Jan 16, 2021 at 1:13 AM Nick Desaulniers
> <nick.desaulniers@gmail.com> wrote:
> >
> > > On Wed, Jan 13, 2021 at 8:07 PM Nick Desaulniers
> > > <ndesaulniers@google.com> wrote:
> > > >
> > > > On Wed, Jan 13, 2021 at 12:55 PM Nathan Chancellor
> > > > <natechancellor@gmail.com> wrote:
> > > > >
> > > > > However, I see an issue with actually using the data:
> > > > >
> > > > > $ sudo -s
> > > > > # mount -t debugfs none /sys/kernel/debug
> > > > > # cp -a /sys/kernel/debug/pgo/profraw vmlinux.profraw
> > > > > # chown nathan:nathan vmlinux.profraw
> > > > > # exit
> > > > > $ tc-build/build/llvm/stage1/bin/llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> > > > > warning: vmlinux.profraw: Invalid instrumentation profile data (bad magic)
> > > > > error: No profiles could be merged.
> > > > >
> > > > > Am I holding it wrong? :) Note, this is virtualized, I do not have any
> > > > > "real" x86 hardware that I can afford to test on right now.
> > > >
> > > > Same.
> > > >
> > > > I think the magic calculation in this patch may differ from upstream
> > > > llvm: https://github.com/llvm/llvm-project/blob/49142991a685bd427d7e877c29c77371dfb7634c/llvm/include/llvm/ProfileData/SampleProf.h#L96-L101
> > >
> > > Err...it looks like it was the padding calculation.  With that fixed
> > > up, we can query the profile data to get insights on the most heavily
> > > called functions.  Here's what my top 20 are (reset, then watch 10
> > > minutes worth of cat videos on youtube while running `find /` and
> > > sleeping at my desk).  Anything curious stand out to anyone?
> >
> > Hello world from my personal laptop whose kernel was rebuilt with
> > profiling data!  Wow, I can run `find /` and watch cat videos on youtube
> > so fast!  Users will love this! /s
> >
> > Checking the sections sizes of .text.hot. and .text.unlikely. looks
> > good!
> >
>
> Is that the latest status of Bill's patch?
>
> Or do you have me a lore link?
>

I tried with the message-id of Bill's initial email:

link="https://lore.kernel.org/r/20210111081821.3041587-1-morbo@google.com"
b4 -d am $link

This gives me:

v4_20210112_morbo_pgo_add_clang_s_profile_guided_optimization_infrastructure.mbx

- Sedat -

>
> [1] https://github.com/gwelymernans/linux/commits/gwelymernans/linux
>
>
> > >
> > > $ llvm-profdata show -topn=20 /tmp/vmlinux.profraw
> > > Instrumentation level: IR  entry_first = 0
> > > Total functions: 48970
> > > Maximum function count: 62070879
> > > Maximum internal block count: 83221158
> > > Top 20 functions with the largest internal block counts:
> > >   drivers/tty/n_tty.c:n_tty_write, max count = 83221158
> > >   rcu_read_unlock_strict, max count = 62070879
> > >   _cond_resched, max count = 25486882
> > >   rcu_all_qs, max count = 25451477
> > >   drivers/cpuidle/poll_state.c:poll_idle, max count = 23618576
> > >   _raw_spin_unlock_irqrestore, max count = 18874121
> > >   drivers/cpuidle/governors/menu.c:menu_select, max count = 18721624
> > >   _raw_spin_lock_irqsave, max count = 18509161
> > >   memchr, max count = 15525452
> > >   _raw_spin_lock, max count = 15484254
> > >   __mod_memcg_state, max count = 14604619
> > >   __mod_memcg_lruvec_state, max count = 14602783
> > >   fs/ext4/hash.c:str2hashbuf_signed, max count = 14098424
> > >   __mod_lruvec_state, max count = 12527154
> > >   __mod_node_page_state, max count = 12525172
> > >   native_sched_clock, max count = 8904692
> > >   sched_clock_cpu, max count = 8895832
> > >   sched_clock, max count = 8894627
> > >   kernel/entry/common.c:exit_to_user_mode_prepare, max count = 8289031
> > >   fpregs_assert_state_consistent, max count = 8287198
> > >
> > > --
> > > Thanks,
> > > ~Nick Desaulniers
> > >
> >
> > --
> > 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/20210116001324.2865-1-nick.desaulniers%40gmail.com.
Sedat Dilek Jan. 18, 2021, 12:57 a.m. UTC | #10
On Sat, Jan 16, 2021 at 1:13 AM Nick Desaulniers
<nick.desaulniers@gmail.com> wrote:
>
> > On Wed, Jan 13, 2021 at 8:07 PM Nick Desaulniers
> > <ndesaulniers@google.com> wrote:
> > >
> > > On Wed, Jan 13, 2021 at 12:55 PM Nathan Chancellor
> > > <natechancellor@gmail.com> wrote:
> > > >
> > > > However, I see an issue with actually using the data:
> > > >
> > > > $ sudo -s
> > > > # mount -t debugfs none /sys/kernel/debug
> > > > # cp -a /sys/kernel/debug/pgo/profraw vmlinux.profraw
> > > > # chown nathan:nathan vmlinux.profraw
> > > > # exit
> > > > $ tc-build/build/llvm/stage1/bin/llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> > > > warning: vmlinux.profraw: Invalid instrumentation profile data (bad magic)
> > > > error: No profiles could be merged.
> > > >
> > > > Am I holding it wrong? :) Note, this is virtualized, I do not have any
> > > > "real" x86 hardware that I can afford to test on right now.
> > >
> > > Same.
> > >
> > > I think the magic calculation in this patch may differ from upstream
> > > llvm: https://github.com/llvm/llvm-project/blob/49142991a685bd427d7e877c29c77371dfb7634c/llvm/include/llvm/ProfileData/SampleProf.h#L96-L101
> >
> > Err...it looks like it was the padding calculation.  With that fixed
> > up, we can query the profile data to get insights on the most heavily
> > called functions.  Here's what my top 20 are (reset, then watch 10
> > minutes worth of cat videos on youtube while running `find /` and
> > sleeping at my desk).  Anything curious stand out to anyone?
>
> Hello world from my personal laptop whose kernel was rebuilt with
> profiling data!  Wow, I can run `find /` and watch cat videos on youtube
> so fast!  Users will love this! /s
>
> Checking the sections sizes of .text.hot. and .text.unlikely. looks
> good!
>

On each rebuild I need to pass to make ...?

   LLVM=1 -fprofile-use=vmlinux.profdata

Did you try together with passing LLVM_IAS=1 to make?

- Sedat -


> >
> > $ llvm-profdata show -topn=20 /tmp/vmlinux.profraw
> > Instrumentation level: IR  entry_first = 0
> > Total functions: 48970
> > Maximum function count: 62070879
> > Maximum internal block count: 83221158
> > Top 20 functions with the largest internal block counts:
> >   drivers/tty/n_tty.c:n_tty_write, max count = 83221158
> >   rcu_read_unlock_strict, max count = 62070879
> >   _cond_resched, max count = 25486882
> >   rcu_all_qs, max count = 25451477
> >   drivers/cpuidle/poll_state.c:poll_idle, max count = 23618576
> >   _raw_spin_unlock_irqrestore, max count = 18874121
> >   drivers/cpuidle/governors/menu.c:menu_select, max count = 18721624
> >   _raw_spin_lock_irqsave, max count = 18509161
> >   memchr, max count = 15525452
> >   _raw_spin_lock, max count = 15484254
> >   __mod_memcg_state, max count = 14604619
> >   __mod_memcg_lruvec_state, max count = 14602783
> >   fs/ext4/hash.c:str2hashbuf_signed, max count = 14098424
> >   __mod_lruvec_state, max count = 12527154
> >   __mod_node_page_state, max count = 12525172
> >   native_sched_clock, max count = 8904692
> >   sched_clock_cpu, max count = 8895832
> >   sched_clock, max count = 8894627
> >   kernel/entry/common.c:exit_to_user_mode_prepare, max count = 8289031
> >   fpregs_assert_state_consistent, max count = 8287198
> >
> > --
> > Thanks,
> > ~Nick Desaulniers
> >
>
> --
> 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/20210116001324.2865-1-nick.desaulniers%40gmail.com.
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..b7f11d8405b73
--- /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 LLVM=1 KCFLAGS=-fprofile-use=vmlinux.profdata ...
diff --git a/MAINTAINERS b/MAINTAINERS
index cc1e6a5ee6e67..1b979da316fa4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -13954,6 +13954,15 @@  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 9e73f82e0d863..9128bfe1ccc97 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 24862d15f3a36..f39d3991f6bfe 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1112,6 +1112,7 @@  config ARCH_SPLIT_ARG64
 	   pairs of 32-bit arguments, select this option.
 
 source "kernel/gcov/Kconfig"
+source "kernel/pgo/Kconfig"
 
 source "scripts/gcc-plugins/Kconfig"
 
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 21f851179ff08..36305ea61dc09 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -96,6 +96,7 @@  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/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..6084ff0652e85
--- /dev/null
+++ b/kernel/pgo/instrument.c
@@ -0,0 +1,185 @@ 
+// 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/bitops.h>
+#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);
+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);
+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);
+
+static u64 inst_prof_get_range_rep_value(u64 value)
+{
+	if (value <= 8)
+		/* The first ranges are individually tracked, us it as is. */
+		return value;
+	else if (value >= 513)
+		/* The last range is mapped to its lowest value. */
+		return 513;
+	else if (hweight64(value) == 1)
+		/* If it's a power of two, use it as is. */
+		return value;
+
+	/* Otherwise, take to the previous power of two + 1. */
+	return (1 << (64 - __builtin_clzll(value) - 1)) + 1;
+}
+
+/*
+ * The target values are partitioned into multiple ranges. The range spec is
+ * defined in compiler-rt/include/profile/InstrProfData.inc.
+ */
+void __llvm_profile_instrument_memop(u64 target_value, void *data,
+				     u32 counter_index);
+void __llvm_profile_instrument_memop(u64 target_value, void *data,
+				     u32 counter_index)
+{
+	u64 rep_value;
+
+	/* Map the target value to the representative value of its range. */
+	rep_value = inst_prof_get_range_rep_value(target_value);
+	__llvm_profile_instrument_target(rep_value, data, counter_index);
+}
+EXPORT_SYMBOL(__llvm_profile_instrument_memop);
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)