From patchwork Sat Nov 2 17:51:08 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Rong Xu X-Patchwork-Id: 13860210 Received: from mail-yb1-f202.google.com (mail-yb1-f202.google.com [209.85.219.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F19361AB50C for ; Sat, 2 Nov 2024 17:51:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.219.202 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730569884; cv=none; b=bbgp9vb/jno5VqzQOhd66g2BhOgyYeF3xcrwzDysJmIZSRu5PuLunKbQAv/NmHnyeWhQRTUhgIY/gHhbzO2i3kT/hg63j9w1Witn8jf9IlKuUJb77+8Xo6vWhVAgXhM+AuOldirVm7gicTh/tt+sD3nZWRHQikKL9yW0SwqkXXc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730569884; c=relaxed/simple; bh=NQcMIzhHS/i4dX02FKwAQavOajDMRCfrWXg9ShLKqtM=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=CowSgDOLS/4psCm+XWLHk6VT07OW/Fsacy5PUdnDI4pr3du6kK02AXB3qLzGSdJzSnqwE2juapAtDPS7HYrSXjCG65nGWT97W8lHmDgZkgQVy4CgE0PSIqdcDV438IlcZT+qTTUH4ZSGUP0zJjyBytzHbXDL69Ka6M2ja8yAj5g= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--xur.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=hj6btU8m; arc=none smtp.client-ip=209.85.219.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--xur.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="hj6btU8m" Received: by mail-yb1-f202.google.com with SMTP id 3f1490d57ef6-e28fc8902e6so5794164276.0 for ; Sat, 02 Nov 2024 10:51:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1730569881; x=1731174681; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:from:to:cc:subject:date:message-id :reply-to; bh=WFRiv2+i6AFQS2QEzRoAvbjmwIKPbZQROYxNZV26DhA=; b=hj6btU8mVbeG9vZtR0Wy1tHX7oj18nwy2LjeJDQJLLvWWe6JC9W9nkXYpQ+VPhRXkr UoBs99Wny/H9PBp8XtpGqNPLXjAviUse2sgcROROBSuEuwDHwyIRQgIkERHbiunUngMg EiF2W53dxNZiWfHB6Klksov21RIiOOyeLtGDfA1UK5aLjqMGit94+qSWqf055JLp3A/v 46HVsGzojMrCggwrJ2D4lrJkddXWyHAABAh1PeaTI/sBch2r5bFu00C67Nj6W/VC5kKu 8bFnE3n3YmXwDcfTMwNZz24ROon517jHOztQdUU3errUIqMQQ1aAIdE4Xynkhpt2+M/a zmMg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1730569881; x=1731174681; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=WFRiv2+i6AFQS2QEzRoAvbjmwIKPbZQROYxNZV26DhA=; b=QsZ7cJ15rUxcDJXH8hAUdE9PabObAPqXPMixUOhONHKhRuhBUmgdmtY+Pjc1FoqG2E 0W/gJK1fsQSVncZ7EEfk4HjxImWjeP2ZZD9FMxP9pjsUuHMl25CtnIJhPqgw3q/kvZTi n39pnnfYP361SuQ1v4zzYkoO+t2RI88U17GJ+g77DYCv++Mzc6SYjzEiEELAVV7YjoTS ow35yCTewwMLR/mkmbfNAZNhW5KDr4ZuF+VExVmhVKHakJyuYAeA415vHFvaZX3lCgJh vjLeB9OO3r+M8CnDPh1AHEImWouVn3PvrEt71l1nG58oIwQ5bXO3BEovnHfLMxuqYDUf /xYg== X-Forwarded-Encrypted: i=1; AJvYcCVIQR5ky2SNHXhOvLW0UyazkgX16PBksnZbSqDJFEn0mAqms78zxpUq2mJ9btGylJ27VFdc7Xmb3U3ClFs=@vger.kernel.org X-Gm-Message-State: AOJu0YweR3hVZUZyOttblDD3iyJuxX848sBn95s18PIkuORsI8Ip5i3V V7T62S+8HgvIsVDVya0k9XnT273ORsmm5sOHXXnzfqHf1/JzgIZ/Y9Tfi5d04nM71g== X-Google-Smtp-Source: AGHT+IF02jYvcxB4tNgDRlM+YFDz+naJ6GwPH0WqS1bTAdqEdLBLnf7zdqiBrkI6VKIsSd10Mflfjjo= X-Received: from xur.c.googlers.com ([fda3:e722:ac3:cc00:20:ed76:c0a8:2330]) (user=xur job=sendgmr) by 2002:a25:aa08:0:b0:e30:d561:dad4 with SMTP id 3f1490d57ef6-e30d561de6bmr12027276.2.1730569880529; Sat, 02 Nov 2024 10:51:20 -0700 (PDT) Date: Sat, 2 Nov 2024 10:51:08 -0700 In-Reply-To: <20241102175115.1769468-1-xur@google.com> Precedence: bulk X-Mailing-List: linux-kbuild@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241102175115.1769468-1-xur@google.com> X-Mailer: git-send-email 2.47.0.163.g1226f6d8fa-goog Message-ID: <20241102175115.1769468-2-xur@google.com> Subject: [PATCH v7 1/7] Add AutoFDO support for Clang build From: Rong Xu To: Alice Ryhl , Andrew Morton , Arnd Bergmann , Bill Wendling , Borislav Petkov , Breno Leitao , Brian Gerst , Dave Hansen , David Li , Han Shen , Heiko Carstens , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Jonathan Corbet , Josh Poimboeuf , Juergen Gross , Justin Stitt , Kees Cook , Masahiro Yamada , "Mike Rapoport (IBM)" , Nathan Chancellor , Nick Desaulniers , Nicolas Schier , "Paul E. McKenney" , Peter Zijlstra , Rong Xu , Sami Tolvanen , Thomas Gleixner , Wei Yang , workflows@vger.kernel.org, Miguel Ojeda , Maksim Panchenko , "David S. Miller" , Andreas Larsson , Yonghong Song , Yabin Cui , Krzysztof Pszeniczny , Sriraman Tallam , Stephane Eranian Cc: x86@kernel.org, linux-arch@vger.kernel.org, sparclinux@vger.kernel.org, linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev Add the build support for using Clang's AutoFDO. Building the kernel with AutoFDO does not reduce the optimization level from the compiler. AutoFDO uses hardware sampling to gather information about the frequency of execution of different code paths within a binary. This information is then used to guide the compiler's optimization decisions, resulting in a more efficient binary. Experiments showed that the kernel can improve up to 10% in latency. The support requires a Clang compiler after LLVM 17. This submission is limited to x86 platforms that support PMU features like LBR on Intel machines and AMD Zen3 BRS. Support for SPE on ARM 1, and BRBE on ARM 1 is part of planned future work. Here is an example workflow for AutoFDO kernel: 1) Build the kernel on the host machine with LLVM enabled, for example, $ make menuconfig LLVM=1 Turn on AutoFDO build config: CONFIG_AUTOFDO_CLANG=y With a configuration that has LLVM enabled, use the following command: scripts/config -e AUTOFDO_CLANG After getting the config, build with $ make LLVM=1 2) Install the kernel on the test machine. 3) Run the load tests. The '-c' option in perf specifies the sample event period. We suggest using a suitable prime number, like 500009, for this purpose. For Intel platforms: $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c \ -o -- For AMD platforms: The supported system are: Zen3 with BRS, or Zen4 with amd_lbr_v2 For Zen3: $ cat proc/cpuinfo | grep " brs" For Zen4: $ cat proc/cpuinfo | grep amd_lbr_v2 $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a \ -N -b -c -o -- 4) (Optional) Download the raw perf file to the host machine. 5) To generate an AutoFDO profile, two offline tools are available: create_llvm_prof and llvm_profgen. The create_llvm_prof tool is part of the AutoFDO project and can be found on GitHub (https://github.com/google/autofdo), version v0.30.1 or later. The llvm_profgen tool is included in the LLVM compiler itself. It's important to note that the version of llvm_profgen doesn't need to match the version of Clang. It needs to be the LLVM 19 release or later, or from the LLVM trunk. $ llvm-profgen --kernel --binary= --perfdata= \ -o or $ create_llvm_prof --binary= --profile= \ --format=extbinary --out= Note that multiple AutoFDO profile files can be merged into one via: $ llvm-profdata merge -o ... 6) Rebuild the kernel using the AutoFDO profile file with the same config as step 1, (Note CONFIG_AUTOFDO_CLANG needs to be enabled): $ make LLVM=1 CLANG_AUTOFDO_PROFILE= Co-developed-by: Han Shen Signed-off-by: Han Shen Signed-off-by: Rong Xu Suggested-by: Sriraman Tallam Suggested-by: Krzysztof Pszeniczny Suggested-by: Nick Desaulniers Suggested-by: Stephane Eranian Tested-by: Yonghong Song Tested-by: Yabin Cui Tested-by: Nathan Chancellor Reviewed-by: Kees Cook Tested-by: Peter Jung --- Documentation/dev-tools/autofdo.rst | 168 ++++++++++++++++++++++++++++ Documentation/dev-tools/index.rst | 1 + MAINTAINERS | 7 ++ Makefile | 1 + arch/Kconfig | 20 ++++ arch/x86/Kconfig | 1 + scripts/Makefile.autofdo | 22 ++++ scripts/Makefile.lib | 10 ++ tools/objtool/check.c | 1 + 9 files changed, 231 insertions(+) create mode 100644 Documentation/dev-tools/autofdo.rst create mode 100644 scripts/Makefile.autofdo diff --git a/Documentation/dev-tools/autofdo.rst b/Documentation/dev-tools/autofdo.rst new file mode 100644 index 0000000000000..1f0a451e9ccd3 --- /dev/null +++ b/Documentation/dev-tools/autofdo.rst @@ -0,0 +1,168 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=================================== +Using AutoFDO with the Linux kernel +=================================== + +This enables AutoFDO build support for the kernel when using +the Clang compiler. AutoFDO (Auto-Feedback-Directed Optimization) +is a type of profile-guided optimization (PGO) used to enhance the +performance of binary executables. It gathers information about the +frequency of execution of various code paths within a binary using +hardware sampling. This data is then used to guide the compiler's +optimization decisions, resulting in a more efficient binary. AutoFDO +is a powerful optimization technique, and data indicates that it can +significantly improve kernel performance. It's especially beneficial +for workloads affected by front-end stalls. + +For AutoFDO builds, unlike non-FDO builds, the user must supply a +profile. Acquiring an AutoFDO profile can be done in several ways. +AutoFDO profiles are created by converting hardware sampling using +the "perf" tool. It is crucial that the workload used to create these +perf files is representative; they must exhibit runtime +characteristics similar to the workloads that are intended to be +optimized. Failure to do so will result in the compiler optimizing +for the wrong objective. + +The AutoFDO profile often encapsulates the program's behavior. If the +performance-critical codes are architecture-independent, the profile +can be applied across platforms to achieve performance gains. For +instance, using the profile generated on Intel architecture to build +a kernel for AMD architecture can also yield performance improvements. + +There are two methods for acquiring a representative profile: +(1) Sample real workloads using a production environment. +(2) Generate the profile using a representative load test. +When enabling the AutoFDO build configuration without providing an +AutoFDO profile, the compiler only modifies the dwarf information in +the kernel without impacting runtime performance. It's advisable to +use a kernel binary built with the same AutoFDO configuration to +collect the perf profile. While it's possible to use a kernel built +with different options, it may result in inferior performance. + +One can collect profiles using AutoFDO build for the previous kernel. +AutoFDO employs relative line numbers to match the profiles, offering +some tolerance for source changes. This mode is commonly used in a +production environment for profile collection. + +In a profile collection based on a load test, the AutoFDO collection +process consists of the following steps: + +#. Initial build: The kernel is built with AutoFDO options + without a profile. + +#. Profiling: The above kernel is then run with a representative + workload to gather execution frequency data. This data is + collected using hardware sampling, via perf. AutoFDO is most + effective on platforms supporting advanced PMU features like + LBR on Intel machines. + +#. AutoFDO profile generation: Perf output file is converted to + the AutoFDO profile via offline tools. + +The support requires a Clang compiler LLVM 17 or later. + +Preparation +=========== + +Configure the kernel with:: + + CONFIG_AUTOFDO_CLANG=y + +Customization +============= + +The default CONFIG_AUTOFDO_CLANG setting covers kernel space objects for +AutoFDO builds. One can, however, enable or disable AutoFDO build for +individual files and directories by adding a line similar to the following +to the respective kernel Makefile: + +- For enabling a single file (e.g. foo.o) :: + + AUTOFDO_PROFILE_foo.o := y + +- For enabling all files in one directory :: + + AUTOFDO_PROFILE := y + +- For disabling one file :: + + AUTOFDO_PROFILE_foo.o := n + +- For disabling all files in one directory :: + + AUTOFDO_PROFILE := n + +Workflow +======== + +Here is an example workflow for AutoFDO kernel: + +1) Build the kernel on the host machine with LLVM enabled, + for example, :: + + $ make menuconfig LLVM=1 + + Turn on AutoFDO build config:: + + CONFIG_AUTOFDO_CLANG=y + + With a configuration that with LLVM enabled, use the following command:: + + $ scripts/config -e AUTOFDO_CLANG + + After getting the config, build with :: + + $ make LLVM=1 + +2) Install the kernel on the test machine. + +3) Run the load tests. The '-c' option in perf specifies the sample + event period. We suggest using a suitable prime number, like 500009, + for this purpose. + + - For Intel platforms:: + + $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c -o -- + + - For AMD platforms: + + The supported systems are: Zen3 with BRS, or Zen4 with amd_lbr_v2. To check, + + For Zen3:: + + $ cat proc/cpuinfo | grep " brs" + + For Zen4:: + + $ cat proc/cpuinfo | grep amd_lbr_v2 + + The following command generated the perf data file:: + + $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a -N -b -c -o -- + +4) (Optional) Download the raw perf file to the host machine. + +5) To generate an AutoFDO profile, two offline tools are available: + create_llvm_prof and llvm_profgen. The create_llvm_prof tool is part + of the AutoFDO project and can be found on GitHub + (https://github.com/google/autofdo), version v0.30.1 or later. + The llvm_profgen tool is included in the LLVM compiler itself. It's + important to note that the version of llvm_profgen doesn't need to match + the version of Clang. It needs to be the LLVM 19 release of Clang + or later, or just from the LLVM trunk. :: + + $ llvm-profgen --kernel --binary= --perfdata= -o + + or :: + + $ create_llvm_prof --binary= --profile= --format=extbinary --out= + + Note that multiple AutoFDO profile files can be merged into one via:: + + $ llvm-profdata merge -o ... + +6) Rebuild the kernel using the AutoFDO profile file with the same config as step 1, + (Note CONFIG_AUTOFDO_CLANG needs to be enabled):: + + $ make LLVM=1 CLANG_AUTOFDO_PROFILE= diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst index 53d4d124f9c52..6945644f7008a 100644 --- a/Documentation/dev-tools/index.rst +++ b/Documentation/dev-tools/index.rst @@ -34,6 +34,7 @@ Documentation/dev-tools/testing-overview.rst ktap checkuapi gpio-sloppy-logic-analyzer + autofdo .. only:: subproject and html diff --git a/MAINTAINERS b/MAINTAINERS index a274079502426..d6ea49433747a 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -3665,6 +3665,13 @@ F: kernel/audit* F: lib/*audit.c K: \baudit_[a-z_0-9]\+\b +AUTOFDO BUILD +M: Rong Xu +M: Han Shen +S: Supported +F: Documentation/dev-tools/autofdo.rst +F: scripts/Makefile.autofdo + AUXILIARY BUS DRIVER M: Greg Kroah-Hartman R: Dave Ertman diff --git a/Makefile b/Makefile index 5e04e4abffd88..b89d87b5dca79 100644 --- a/Makefile +++ b/Makefile @@ -1018,6 +1018,7 @@ include-$(CONFIG_KMSAN) += scripts/Makefile.kmsan include-$(CONFIG_UBSAN) += scripts/Makefile.ubsan include-$(CONFIG_KCOV) += scripts/Makefile.kcov include-$(CONFIG_RANDSTRUCT) += scripts/Makefile.randstruct +include-$(CONFIG_AUTOFDO_CLANG) += scripts/Makefile.autofdo include-$(CONFIG_GCC_PLUGINS) += scripts/Makefile.gcc-plugins include $(addprefix $(srctree)/, $(include-y)) diff --git a/arch/Kconfig b/arch/Kconfig index bd9f095d69fa0..8dca3b5e6ef53 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -811,6 +811,26 @@ config LTO_CLANG_THIN If unsure, say Y. endchoice +config ARCH_SUPPORTS_AUTOFDO_CLANG + bool + +config AUTOFDO_CLANG + bool "Enable Clang's AutoFDO build (EXPERIMENTAL)" + depends on ARCH_SUPPORTS_AUTOFDO_CLANG + depends on CC_IS_CLANG && CLANG_VERSION >= 170000 + help + This option enables Clang’s AutoFDO build. When + an AutoFDO profile is specified in variable + CLANG_AUTOFDO_PROFILE during the build process, + Clang uses the profile to optimize the kernel. + + If no profile is specified, AutoFDO options are + still passed to Clang to facilitate the collection + of perf data for creating an AutoFDO profile in + subsequent builds. + + If unsure, say N. + config ARCH_SUPPORTS_CFI_CLANG bool help diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 16354dfa6d965..9dc87661fb373 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -126,6 +126,7 @@ config X86 select ARCH_SUPPORTS_LTO_CLANG select ARCH_SUPPORTS_LTO_CLANG_THIN select ARCH_SUPPORTS_RT + select ARCH_SUPPORTS_AUTOFDO_CLANG select ARCH_USE_BUILTIN_BSWAP select ARCH_USE_CMPXCHG_LOCKREF if X86_CMPXCHG64 select ARCH_USE_MEMTEST diff --git a/scripts/Makefile.autofdo b/scripts/Makefile.autofdo new file mode 100644 index 0000000000000..ff96a63fea7cd --- /dev/null +++ b/scripts/Makefile.autofdo @@ -0,0 +1,22 @@ +# SPDX-License-Identifier: GPL-2.0 + +# Enable available and selected Clang AutoFDO features. + +CFLAGS_AUTOFDO_CLANG := -fdebug-info-for-profiling -mllvm -enable-fs-discriminator=true -mllvm -improved-fs-discriminator=true + +ifndef CONFIG_DEBUG_INFO + CFLAGS_AUTOFDO_CLANG += -gmlt +endif + +ifdef CLANG_AUTOFDO_PROFILE + CFLAGS_AUTOFDO_CLANG += -fprofile-sample-use=$(CLANG_AUTOFDO_PROFILE) +endif + +ifdef CONFIG_LTO_CLANG_THIN + ifdef CLANG_AUTOFDO_PROFILE + KBUILD_LDFLAGS += --lto-sample-profile=$(CLANG_AUTOFDO_PROFILE) + endif + KBUILD_LDFLAGS += --mllvm=-enable-fs-discriminator=true --mllvm=-improved-fs-discriminator=true -plugin-opt=thinlto +endif + +export CFLAGS_AUTOFDO_CLANG diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib index 01a9f567d5af4..2d0942c1a0277 100644 --- a/scripts/Makefile.lib +++ b/scripts/Makefile.lib @@ -191,6 +191,16 @@ _c_flags += $(if $(patsubst n%,, \ -D__KCSAN_INSTRUMENT_BARRIERS__) endif +# +# Enable AutoFDO build flags except some files or directories we don't want to +# enable (depends on variables AUTOFDO_PROFILE_obj.o and AUTOFDO_PROFILE). +# +ifeq ($(CONFIG_AUTOFDO_CLANG),y) +_c_flags += $(if $(patsubst n%,, \ + $(AUTOFDO_PROFILE_$(target-stem).o)$(AUTOFDO_PROFILE)$(is-kernel-object)), \ + $(CFLAGS_AUTOFDO_CLANG)) +endif + # $(src) for including checkin headers from generated source files # $(obj) for including generated headers from checkin source files ifeq ($(KBUILD_EXTMOD),) diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 6604f5d038aad..4c5229991e1e0 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -4557,6 +4557,7 @@ static int validate_ibt(struct objtool_file *file) !strcmp(sec->name, "__jump_table") || !strcmp(sec->name, "__mcount_loc") || !strcmp(sec->name, ".kcfi_traps") || + !strcmp(sec->name, ".llvm.call-graph-profile") || strstr(sec->name, "__patchable_function_entries")) continue; 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AJvYcCUc5TA8Nh2wHlzwzCV+1Yk4EuoWORO07456N9/eHry/zvSUvermJQ+MwEbQ39yzHGgH4W01UAJPh2R73Qo=@vger.kernel.org X-Gm-Message-State: AOJu0YyNbjFaWRocvU3IYpN8I63LXYWwv8o82auf6US3bB8g7/picA9d qSn9Xspps9wKxm/lJVBSXUNNMAUvFgRUgvTi1H3o+gpBi6/Ni933YWz+jWMLCXHlmA== X-Google-Smtp-Source: AGHT+IFrvTh9yGQeIC99rDaSyohlIWmY/cd98cXWXWBBtOnvULrh4CKCoiBDwd6yf44KtAXaT7swZbs= X-Received: from xur.c.googlers.com ([fda3:e722:ac3:cc00:20:ed76:c0a8:2330]) (user=xur job=sendgmr) by 2002:a25:a291:0:b0:e28:e510:6ab1 with SMTP id 3f1490d57ef6-e33026b3c56mr4382276.8.1730569882127; Sat, 02 Nov 2024 10:51:22 -0700 (PDT) Date: Sat, 2 Nov 2024 10:51:09 -0700 In-Reply-To: <20241102175115.1769468-1-xur@google.com> Precedence: bulk X-Mailing-List: linux-kbuild@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241102175115.1769468-1-xur@google.com> X-Mailer: git-send-email 2.47.0.163.g1226f6d8fa-goog Message-ID: <20241102175115.1769468-3-xur@google.com> Subject: [PATCH v7 2/7] objtool: Fix unreachable instruction warnings for weak functions From: Rong Xu To: Alice Ryhl , Andrew Morton , Arnd Bergmann , Bill Wendling , Borislav Petkov , Breno Leitao , Brian Gerst , Dave Hansen , David Li , Han Shen , Heiko Carstens , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Jonathan Corbet , Josh Poimboeuf , Juergen Gross , Justin Stitt , Kees Cook , Masahiro Yamada , "Mike Rapoport (IBM)" , Nathan Chancellor , Nick Desaulniers , Nicolas Schier , "Paul E. McKenney" , Peter Zijlstra , Rong Xu , Sami Tolvanen , Thomas Gleixner , Wei Yang , workflows@vger.kernel.org, Miguel Ojeda , Maksim Panchenko , "David S. Miller" , Andreas Larsson , Yonghong Song , Yabin Cui , Krzysztof Pszeniczny , Sriraman Tallam , Stephane Eranian Cc: x86@kernel.org, linux-arch@vger.kernel.org, sparclinux@vger.kernel.org, linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev In the presence of both weak and strong function definitions, the linker drops the weak symbol in favor of a strong symbol, but leaves the code in place. Code in ignore_unreachable_insn() has some heuristics to suppress the warning, but it does not work when -ffunction-sections is enabled. Suppose function foo has both strong and weak definitions. Case 1: The strong definition has an annotated section name, like .init.text. Only the weak definition will be placed into .text.foo. But since the section has no symbols, there will be no "hole" in the section. Case 2: Both sections are without an annotated section name. Both will be placed into .text.foo section, but there will be only one symbol (the strong one). If the weak code is before the strong code, there is no "hole" as it fails to find the right-most symbol before the offset. The fix is to use the first node to compute the hole if hole.sym is empty. If there is no symbol in the section, the first node will be NULL, in which case, -1 is returned to skip the whole section. Co-developed-by: Han Shen Signed-off-by: Han Shen Signed-off-by: Rong Xu Suggested-by: Sriraman Tallam Suggested-by: Krzysztof Pszeniczny Tested-by: Yonghong Song Tested-by: Yabin Cui Tested-by: Nathan Chancellor Reviewed-by: Kees Cook Acked-by: Josh Poimboeuf --- tools/objtool/elf.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c index 3d27983dc908d..6f64d611faea9 100644 --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -224,12 +224,17 @@ int find_symbol_hole_containing(const struct section *sec, unsigned long offset) if (n) return 0; /* not a hole */ - /* didn't find a symbol for which @offset is after it */ - if (!hole.sym) - return 0; /* not a hole */ + /* + * @offset >= sym->offset + sym->len, find symbol after it. + * When hole.sym is empty, use the first node to compute the hole. + * If there is no symbol in the section, the first node will be NULL, + * in which case, -1 is returned to skip the whole section. + */ + if (hole.sym) + n = rb_next(&hole.sym->node); + else + n = rb_first_cached(&sec->symbol_tree); - /* @offset >= sym->offset + sym->len, find symbol after it */ - n = rb_next(&hole.sym->node); if (!n) return -1; /* until end of address space */ From patchwork Sat Nov 2 17:51:10 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Rong Xu X-Patchwork-Id: 13860212 Received: from mail-yw1-f201.google.com (mail-yw1-f201.google.com [209.85.128.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 06F941ABEC9 for ; Sat, 2 Nov 2024 17:51:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730569887; cv=none; b=dUZFxgRNMSv+/8abKZ9KybJLB8rBmwR1wvQb0znbnXM1FpET4YdzWrRV5ii/lJdU+vyqRmELeL2loMlwGxmKUqeyjoBZmNCTTz5xKZ/CmOay0WwBSLatSyTug1zGTRiVT98m5GWhhWMFRhh63agwQxLOJmQ7ggHwNYWgxLLGW6Y= ARC-Message-Signature: i=1; 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Peter Anvin" , Ingo Molnar , Jann Horn , Jonathan Corbet , Josh Poimboeuf , Juergen Gross , Justin Stitt , Kees Cook , Masahiro Yamada , "Mike Rapoport (IBM)" , Nathan Chancellor , Nick Desaulniers , Nicolas Schier , "Paul E. McKenney" , Peter Zijlstra , Rong Xu , Sami Tolvanen , Thomas Gleixner , Wei Yang , workflows@vger.kernel.org, Miguel Ojeda , Maksim Panchenko , "David S. Miller" , Andreas Larsson , Yonghong Song , Yabin Cui , Krzysztof Pszeniczny , Sriraman Tallam , Stephane Eranian Cc: x86@kernel.org, linux-arch@vger.kernel.org, sparclinux@vger.kernel.org, linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev When the -ffunction-sections compiler option is enabled, each function is placed in a separate section named .text.function_name rather than putting all functions in a single .text section. However, using -function-sections can cause problems with the linker script. The comments included in include/asm-generic/vmlinux.lds.h note these issues.: “TEXT_MAIN here will match .text.fixup and .text.unlikely if dead code elimination is enabled, so these sections should be converted to use ".." first.” It is unclear whether there is a straightforward method for converting a suffix to "..". This patch modifies the order of subsections within the text output section. Specifically, it changes current order: .text.hot, .text, .text_unlikely, .text.unknown, .text.asan to the new order: .text.asan, .text.unknown, .text_unlikely, .text.hot, .text Here is the rationale behind the new layout: The majority of the code resides in three sections: .text.hot, .text, and .text.unlikely, with .text.unknown containing a negligible amount. .text.asan is only generated in ASAN builds. The primary goal is to group code segments based on their execution frequency (hotness). First, we want to place .text.hot adjacent to .text. Since we cannot put .text.hot after .text (Due to constraints with -ffunction-sections, placing .text.hot after .text is problematic), we need to put .text.hot before .text. Then it comes to .text.unlikely, we cannot put it after .text (same -ffunction-sections issue) . Therefore, we position .text.unlikely before .text.hot. .text.unknown and .tex.asan follow the same logic. This revised ordering effectively reverses the original arrangement (for .text.unlikely, .text.unknown, and .tex.asan), maintaining a similar level of affinity between sections. It also places .text.hot section at the beginning of a page to better utilize the TLB entry. Note that the limitation arises because the linker script employs glob patterns instead of regular expressions for string matching. While there is a method to maintain the current order using complex patterns, this significantly complicates the pattern and increases the likelihood of errors. This patch also changes vmlinux.lds.S for the sparc64 architecture to accommodate specific symbol placement requirements. Co-developed-by: Han Shen Signed-off-by: Han Shen Signed-off-by: Rong Xu Suggested-by: Sriraman Tallam Suggested-by: Krzysztof Pszeniczny Tested-by: Yonghong Song Tested-by: Yabin Cui Tested-by: Nathan Chancellor Reviewed-by: Kees Cook --- arch/sparc/kernel/vmlinux.lds.S | 5 +++++ include/asm-generic/vmlinux.lds.h | 19 ++++++++++++------- 2 files changed, 17 insertions(+), 7 deletions(-) diff --git a/arch/sparc/kernel/vmlinux.lds.S b/arch/sparc/kernel/vmlinux.lds.S index d317a843f7ea9..f1b86eb303404 100644 --- a/arch/sparc/kernel/vmlinux.lds.S +++ b/arch/sparc/kernel/vmlinux.lds.S @@ -48,6 +48,11 @@ SECTIONS { _text = .; HEAD_TEXT + ALIGN_FUNCTION(); +#ifdef CONFIG_SPARC64 + /* Match text section symbols in head_64.S first */ + *head_64.o(.text) +#endif TEXT_TEXT SCHED_TEXT LOCK_TEXT diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index eeadbaeccf88b..fd901951549c0 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -553,19 +553,24 @@ * .text section. Map to function alignment to avoid address changes * during second ld run in second ld pass when generating System.map * - * TEXT_MAIN here will match .text.fixup and .text.unlikely if dead - * code elimination is enabled, so these sections should be converted - * to use ".." first. + * TEXT_MAIN here will match symbols with a fixed pattern (for example, + * .text.hot or .text.unlikely) if dead code elimination or + * function-section is enabled. Match these symbols first before + * TEXT_MAIN to ensure they are grouped together. + * + * Also placing .text.hot section at the beginning of a page, this + * would help the TLB performance. */ #define TEXT_TEXT \ ALIGN_FUNCTION(); \ + *(.text.asan.* .text.tsan.*) \ + *(.text.unknown .text.unknown.*) \ + *(.text.unlikely .text.unlikely.*) \ + . = ALIGN(PAGE_SIZE); \ *(.text.hot .text.hot.*) \ *(TEXT_MAIN .text.fixup) \ - *(.text.unlikely .text.unlikely.*) \ - *(.text.unknown .text.unknown.*) \ NOINSTR_TEXT \ - *(.ref.text) \ - *(.text.asan.* .text.tsan.*) + *(.ref.text) /* sched.text is aling to function alignment to secure we have same From patchwork Sat Nov 2 17:51:11 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Rong Xu X-Patchwork-Id: 13860213 Received: from mail-yw1-f201.google.com (mail-yw1-f201.google.com [209.85.128.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4E05C1AC42B for ; 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Sat, 02 Nov 2024 10:51:25 -0700 (PDT) Date: Sat, 2 Nov 2024 10:51:11 -0700 In-Reply-To: <20241102175115.1769468-1-xur@google.com> Precedence: bulk X-Mailing-List: linux-kbuild@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241102175115.1769468-1-xur@google.com> X-Mailer: git-send-email 2.47.0.163.g1226f6d8fa-goog Message-ID: <20241102175115.1769468-5-xur@google.com> Subject: [PATCH v7 4/7] Add markers for text_unlikely and text_hot sections From: Rong Xu To: Alice Ryhl , Andrew Morton , Arnd Bergmann , Bill Wendling , Borislav Petkov , Breno Leitao , Brian Gerst , Dave Hansen , David Li , Han Shen , Heiko Carstens , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Jonathan Corbet , Josh Poimboeuf , Juergen Gross , Justin Stitt , Kees Cook , Masahiro Yamada , "Mike Rapoport (IBM)" , Nathan Chancellor , Nick Desaulniers , Nicolas Schier , "Paul E. McKenney" , Peter Zijlstra , Rong Xu , Sami Tolvanen , Thomas Gleixner , Wei Yang , workflows@vger.kernel.org, Miguel Ojeda , Maksim Panchenko , "David S. Miller" , Andreas Larsson , Yonghong Song , Yabin Cui , Krzysztof Pszeniczny , Sriraman Tallam , Stephane Eranian Cc: x86@kernel.org, linux-arch@vger.kernel.org, sparclinux@vger.kernel.org, linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev Add markers like __hot_text_start, __hot_text_end, __unlikely_text_start, and __unlikely_text_end which will be included in System.map. These markers indicate how the compiler groups functions, providing valuable information to developers about the layout and optimization of the code. Co-developed-by: Han Shen Signed-off-by: Han Shen Signed-off-by: Rong Xu Suggested-by: Sriraman Tallam Tested-by: Yonghong Song Tested-by: Yabin Cui Tested-by: Nathan Chancellor Reviewed-by: Kees Cook --- include/asm-generic/vmlinux.lds.h | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index fd901951549c0..e02973f3b4189 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -549,6 +549,16 @@ __cpuidle_text_end = .; \ __noinstr_text_end = .; +#define TEXT_UNLIKELY \ + __unlikely_text_start = .; \ + *(.text.unlikely .text.unlikely.*) \ + __unlikely_text_end = .; + +#define TEXT_HOT \ + __hot_text_start = .; \ + *(.text.hot .text.hot.*) \ + __hot_text_end = .; + /* * .text section. Map to function alignment to avoid address changes * during second ld run in second ld pass when generating System.map @@ -565,9 +575,9 @@ ALIGN_FUNCTION(); \ *(.text.asan.* .text.tsan.*) \ *(.text.unknown .text.unknown.*) \ - *(.text.unlikely .text.unlikely.*) \ + TEXT_UNLIKELY \ . = ALIGN(PAGE_SIZE); \ - *(.text.hot .text.hot.*) \ + TEXT_HOT \ *(TEXT_MAIN .text.fixup) \ NOINSTR_TEXT \ *(.ref.text) From patchwork Sat Nov 2 17:51:12 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Rong Xu X-Patchwork-Id: 13860214 Received: from mail-yw1-f201.google.com (mail-yw1-f201.google.com [209.85.128.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 033EC1ABEC7 for ; Sat, 2 Nov 2024 17:51:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.201 ARC-Seal: i=1; a=rsa-sha256; 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Sat, 02 Nov 2024 10:51:26 -0700 (PDT) Date: Sat, 2 Nov 2024 10:51:12 -0700 In-Reply-To: <20241102175115.1769468-1-xur@google.com> Precedence: bulk X-Mailing-List: linux-kbuild@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241102175115.1769468-1-xur@google.com> X-Mailer: git-send-email 2.47.0.163.g1226f6d8fa-goog Message-ID: <20241102175115.1769468-6-xur@google.com> Subject: [PATCH v7 5/7] AutoFDO: Enable -ffunction-sections for the AutoFDO build From: Rong Xu To: Alice Ryhl , Andrew Morton , Arnd Bergmann , Bill Wendling , Borislav Petkov , Breno Leitao , Brian Gerst , Dave Hansen , David Li , Han Shen , Heiko Carstens , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Jonathan Corbet , Josh Poimboeuf , Juergen Gross , Justin Stitt , Kees Cook , Masahiro Yamada , "Mike Rapoport (IBM)" , Nathan Chancellor , Nick Desaulniers , Nicolas Schier , "Paul E. McKenney" , Peter Zijlstra , Rong Xu , Sami Tolvanen , Thomas Gleixner , Wei Yang , workflows@vger.kernel.org, Miguel Ojeda , Maksim Panchenko , "David S. Miller" , Andreas Larsson , Yonghong Song , Yabin Cui , Krzysztof Pszeniczny , Sriraman Tallam , Stephane Eranian Cc: x86@kernel.org, linux-arch@vger.kernel.org, sparclinux@vger.kernel.org, linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev Enable -ffunction-sections by default for the AutoFDO build. With -ffunction-sections, the compiler places each function in its own section named .text.function_name instead of placing all functions in the .text section. In the AutoFDO build, this allows the linker to utilize profile information to reorganize functions for improved utilization of iCache and iTLB. Co-developed-by: Han Shen Signed-off-by: Han Shen Signed-off-by: Rong Xu Suggested-by: Sriraman Tallam Tested-by: Yonghong Song Tested-by: Yabin Cui Tested-by: Nathan Chancellor Reviewed-by: Kees Cook --- include/asm-generic/vmlinux.lds.h | 11 +++++++++-- scripts/Makefile.autofdo | 2 +- 2 files changed, 10 insertions(+), 3 deletions(-) diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index e02973f3b4189..bd64fdedabd2f 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -95,18 +95,25 @@ * With LTO_CLANG, the linker also splits sections by default, so we need * these macros to combine the sections during the final link. * + * With AUTOFDO_CLANG, by default, the linker splits text sections and + * regroups functions into subsections. + * * RODATA_MAIN is not used because existing code already defines .rodata.x * sections to be brought in with rodata. */ -#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) +#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) || \ +defined(CONFIG_AUTOFDO_CLANG) #define TEXT_MAIN .text .text.[0-9a-zA-Z_]* +#else +#define TEXT_MAIN .text +#endif +#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) #define DATA_MAIN .data .data.[0-9a-zA-Z_]* .data..L* .data..compoundliteral* .data.$__unnamed_* .data.$L* #define SDATA_MAIN .sdata .sdata.[0-9a-zA-Z_]* #define RODATA_MAIN .rodata .rodata.[0-9a-zA-Z_]* .rodata..L* #define BSS_MAIN .bss .bss.[0-9a-zA-Z_]* .bss..L* .bss..compoundliteral* #define SBSS_MAIN .sbss .sbss.[0-9a-zA-Z_]* #else -#define TEXT_MAIN .text #define DATA_MAIN .data #define SDATA_MAIN .sdata #define RODATA_MAIN .rodata diff --git a/scripts/Makefile.autofdo b/scripts/Makefile.autofdo index ff96a63fea7cd..6155d6fc4ca7f 100644 --- a/scripts/Makefile.autofdo +++ b/scripts/Makefile.autofdo @@ -9,7 +9,7 @@ ifndef CONFIG_DEBUG_INFO endif ifdef CLANG_AUTOFDO_PROFILE - CFLAGS_AUTOFDO_CLANG += -fprofile-sample-use=$(CLANG_AUTOFDO_PROFILE) + CFLAGS_AUTOFDO_CLANG += -fprofile-sample-use=$(CLANG_AUTOFDO_PROFILE) -ffunction-sections endif ifdef CONFIG_LTO_CLANG_THIN From patchwork Sat Nov 2 17:51:13 2024 Content-Type: text/plain; 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Peter Anvin" , Ingo Molnar , Jann Horn , Jonathan Corbet , Josh Poimboeuf , Juergen Gross , Justin Stitt , Kees Cook , Masahiro Yamada , "Mike Rapoport (IBM)" , Nathan Chancellor , Nick Desaulniers , Nicolas Schier , "Paul E. McKenney" , Peter Zijlstra , Rong Xu , Sami Tolvanen , Thomas Gleixner , Wei Yang , workflows@vger.kernel.org, Miguel Ojeda , Maksim Panchenko , "David S. Miller" , Andreas Larsson , Yonghong Song , Yabin Cui , Krzysztof Pszeniczny , Sriraman Tallam , Stephane Eranian Cc: x86@kernel.org, linux-arch@vger.kernel.org, sparclinux@vger.kernel.org, linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev Enable the machine function split optimization for AutoFDO in Clang. Machine function split (MFS) is a pass in the Clang compiler that splits a function into hot and cold parts. The linker groups all cold blocks across functions together. This decreases hot code fragmentation and improves iCache and iTLB utilization. MFS requires a profile so this is enabled only for the AutoFDO builds. Co-developed-by: Han Shen Signed-off-by: Han Shen Signed-off-by: Rong Xu Suggested-by: Sriraman Tallam Suggested-by: Krzysztof Pszeniczny Tested-by: Yonghong Song Tested-by: Yabin Cui Tested-by: Nathan Chancellor Reviewed-by: Kees Cook --- include/asm-generic/vmlinux.lds.h | 7 ++++++- scripts/Makefile.autofdo | 2 ++ 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index bd64fdedabd2f..8a0bb3946cf05 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -556,6 +556,11 @@ defined(CONFIG_AUTOFDO_CLANG) __cpuidle_text_end = .; \ __noinstr_text_end = .; +#define TEXT_SPLIT \ + __split_text_start = .; \ + *(.text.split .text.split.[0-9a-zA-Z_]*) \ + __split_text_end = .; + #define TEXT_UNLIKELY \ __unlikely_text_start = .; \ *(.text.unlikely .text.unlikely.*) \ @@ -582,6 +587,7 @@ defined(CONFIG_AUTOFDO_CLANG) ALIGN_FUNCTION(); \ *(.text.asan.* .text.tsan.*) \ *(.text.unknown .text.unknown.*) \ + TEXT_SPLIT \ TEXT_UNLIKELY \ . = ALIGN(PAGE_SIZE); \ TEXT_HOT \ @@ -589,7 +595,6 @@ defined(CONFIG_AUTOFDO_CLANG) NOINSTR_TEXT \ *(.ref.text) - /* sched.text is aling to function alignment to secure we have same * address even at second ld pass when generating System.map */ #define SCHED_TEXT \ diff --git a/scripts/Makefile.autofdo b/scripts/Makefile.autofdo index 6155d6fc4ca7f..1caf2457e585c 100644 --- a/scripts/Makefile.autofdo +++ b/scripts/Makefile.autofdo @@ -10,6 +10,7 @@ endif ifdef CLANG_AUTOFDO_PROFILE CFLAGS_AUTOFDO_CLANG += -fprofile-sample-use=$(CLANG_AUTOFDO_PROFILE) -ffunction-sections + CFLAGS_AUTOFDO_CLANG += -fsplit-machine-functions endif ifdef CONFIG_LTO_CLANG_THIN @@ -17,6 +18,7 @@ ifdef CONFIG_LTO_CLANG_THIN KBUILD_LDFLAGS += --lto-sample-profile=$(CLANG_AUTOFDO_PROFILE) endif KBUILD_LDFLAGS += --mllvm=-enable-fs-discriminator=true --mllvm=-improved-fs-discriminator=true -plugin-opt=thinlto + KBUILD_LDFLAGS += -plugin-opt=-split-machine-functions endif export CFLAGS_AUTOFDO_CLANG From patchwork Sat Nov 2 17:51:14 2024 Content-Type: text/plain; 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AJvYcCUEmZrdm+3wFva31uaC3h3gec3fyMqZu+D3HmUSyvdOMydx+rs0QLGIvhy4K5uWu+1WIHeKsjqlg7LcIJY=@vger.kernel.org X-Gm-Message-State: AOJu0YwZN56ZG0M3sO6T1Q6WqWfMvczS+fLm6g3XVIwVUJlFVfQxMyfT tthgplr6AblFEntSvGDZUdZ73BO5bfFH244HbdU8jcbESmPZKwl3+L0s76+kgUNEIw== X-Google-Smtp-Source: AGHT+IEZ+AxDqMwv1T8/N6VbPHxXAJQIxGK0//+kNZzPq9Tu/0rNxZacImTwdovzsKaod3QXHJCzhKg= X-Received: from xur.c.googlers.com ([fda3:e722:ac3:cc00:20:ed76:c0a8:2330]) (user=xur job=sendgmr) by 2002:a25:26d1:0:b0:e2b:d0e9:130f with SMTP id 3f1490d57ef6-e30cf2e9c2bmr10994276.0.1730569890149; Sat, 02 Nov 2024 10:51:30 -0700 (PDT) Date: Sat, 2 Nov 2024 10:51:14 -0700 In-Reply-To: <20241102175115.1769468-1-xur@google.com> Precedence: bulk X-Mailing-List: linux-kbuild@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241102175115.1769468-1-xur@google.com> X-Mailer: git-send-email 2.47.0.163.g1226f6d8fa-goog Message-ID: <20241102175115.1769468-8-xur@google.com> Subject: [PATCH v7 7/7] Add Propeller configuration for kernel build From: Rong Xu To: Alice Ryhl , Andrew Morton , Arnd Bergmann , Bill Wendling , Borislav Petkov , Breno Leitao , Brian Gerst , Dave Hansen , David Li , Han Shen , Heiko Carstens , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Jonathan Corbet , Josh Poimboeuf , Juergen Gross , Justin Stitt , Kees Cook , Masahiro Yamada , "Mike Rapoport (IBM)" , Nathan Chancellor , Nick Desaulniers , Nicolas Schier , "Paul E. McKenney" , Peter Zijlstra , Rong Xu , Sami Tolvanen , Thomas Gleixner , Wei Yang , workflows@vger.kernel.org, Miguel Ojeda , Maksim Panchenko , "David S. Miller" , Andreas Larsson , Yonghong Song , Yabin Cui , Krzysztof Pszeniczny , Sriraman Tallam , Stephane Eranian Cc: x86@kernel.org, linux-arch@vger.kernel.org, sparclinux@vger.kernel.org, linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev Add the build support for using Clang's Propeller optimizer. Like AutoFDO, Propeller uses hardware sampling to gather information about the frequency of execution of different code paths within a binary. This information is then used to guide the compiler's optimization decisions, resulting in a more efficient binary. The support requires a Clang compiler LLVM 19 or later, and the create_llvm_prof tool (https://github.com/google/autofdo/releases/tag/v0.30.1). This commit is limited to x86 platforms that support PMU features like LBR on Intel machines and AMD Zen3 BRS. Here is an example workflow for building an AutoFDO+Propeller optimized kernel: 1) Build the kernel on the host machine, with AutoFDO and Propeller build config CONFIG_AUTOFDO_CLANG=y CONFIG_PROPELLER_CLANG=y then $ make LLVM=1 CLANG_AUTOFDO_PROFILE= “” is the profile collected when doing a non-Propeller AutoFDO build. This step builds a kernel that has the same optimization level as AutoFDO, plus a metadata section that records basic block information. This kernel image runs as fast as an AutoFDO optimized kernel. 2) Install the kernel on test/production machines. 3) Run the load tests. The '-c' option in perf specifies the sample event period. We suggest using a suitable prime number, like 500009, for this purpose. For Intel platforms: $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c \ -o -- For AMD platforms: The supported system are: Zen3 with BRS, or Zen4 with amd_lbr_v2 # To see if Zen3 support LBR: $ cat proc/cpuinfo | grep " brs" # To see if Zen4 support LBR: $ cat proc/cpuinfo | grep amd_lbr_v2 # If the result is yes, then collect the profile using: $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a \ -N -b -c -o -- 4) (Optional) Download the raw perf file to the host machine. 5) Generate Propeller profile: $ create_llvm_prof --binary= --profile= \ --format=propeller --propeller_output_module_name \ --out=_cc_profile.txt \ --propeller_symorder=_ld_profile.txt “create_llvm_prof” is the profile conversion tool, and a prebuilt binary for linux can be found on https://github.com/google/autofdo/releases/tag/v0.30.1 (can also build from source). "" can be something like "/home/user/dir/any_string". This command generates a pair of Propeller profiles: "_cc_profile.txt" and "_ld_profile.txt". 6) Rebuild the kernel using the AutoFDO and Propeller profile files. CONFIG_AUTOFDO_CLANG=y CONFIG_PROPELLER_CLANG=y and $ make LLVM=1 CLANG_AUTOFDO_PROFILE= \ CLANG_PROPELLER_PROFILE_PREFIX= Co-developed-by: Han Shen Signed-off-by: Han Shen Signed-off-by: Rong Xu Suggested-by: Sriraman Tallam Suggested-by: Krzysztof Pszeniczny Suggested-by: Nick Desaulniers Suggested-by: Stephane Eranian Tested-by: Yonghong Song Tested-by: Nathan Chancellor Reviewed-by: Kees Cook --- Documentation/dev-tools/index.rst | 1 + Documentation/dev-tools/propeller.rst | 162 ++++++++++++++++++++++++++ MAINTAINERS | 7 ++ Makefile | 1 + arch/Kconfig | 19 +++ arch/x86/Kconfig | 1 + arch/x86/kernel/vmlinux.lds.S | 4 + include/asm-generic/vmlinux.lds.h | 6 +- scripts/Makefile.lib | 10 ++ scripts/Makefile.propeller | 28 +++++ tools/objtool/check.c | 1 + 11 files changed, 237 insertions(+), 3 deletions(-) create mode 100644 Documentation/dev-tools/propeller.rst create mode 100644 scripts/Makefile.propeller diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst index 6945644f7008a..3c0ac08b27091 100644 --- a/Documentation/dev-tools/index.rst +++ b/Documentation/dev-tools/index.rst @@ -35,6 +35,7 @@ Documentation/dev-tools/testing-overview.rst checkuapi gpio-sloppy-logic-analyzer autofdo + propeller .. only:: subproject and html diff --git a/Documentation/dev-tools/propeller.rst b/Documentation/dev-tools/propeller.rst new file mode 100644 index 0000000000000..92195958e3dbc --- /dev/null +++ b/Documentation/dev-tools/propeller.rst @@ -0,0 +1,162 @@ +.. SPDX-License-Identifier: GPL-2.0 + +===================================== +Using Propeller with the Linux kernel +===================================== + +This enables Propeller build support for the kernel when using Clang +compiler. Propeller is a profile-guided optimization (PGO) method used +to optimize binary executables. Like AutoFDO, it utilizes hardware +sampling to gather information about the frequency of execution of +different code paths within a binary. Unlike AutoFDO, this information +is then used right before linking phase to optimize (among others) +block layout within and across functions. + +A few important notes about adopting Propeller optimization: + +#. Although it can be used as a standalone optimization step, it is + strongly recommended to apply Propeller on top of AutoFDO, + AutoFDO+ThinLTO or Instrument FDO. The rest of this document + assumes this paradigm. + +#. Propeller uses another round of profiling on top of + AutoFDO/AutoFDO+ThinLTO/iFDO. The whole build process involves + "build-afdo - train-afdo - build-propeller - train-propeller - + build-optimized". + +#. Propeller requires LLVM 19 release or later for Clang/Clang++ + and the linker(ld.lld). + +#. In addition to LLVM toolchain, Propeller requires a profiling + conversion tool: https://github.com/google/autofdo with a release + after v0.30.1: https://github.com/google/autofdo/releases/tag/v0.30.1. + +The Propeller optimization process involves the following steps: + +#. Initial building: Build the AutoFDO or AutoFDO+ThinLTO binary as + you would normally do, but with a set of compile-time / link-time + flags, so that a special metadata section is created within the + kernel binary. The special section is only intend to be used by the + profiling tool, it is not part of the runtime image, nor does it + change kernel run time text sections. + +#. Profiling: The above kernel is then run with a representative + workload to gather execution frequency data. This data is collected + using hardware sampling, via perf. Propeller is most effective on + platforms supporting advanced PMU features like LBR on Intel + machines. This step is the same as profiling the kernel for AutoFDO + (the exact perf parameters can be different). + +#. Propeller profile generation: Perf output file is converted to a + pair of Propeller profiles via an offline tool. + +#. Optimized build: Build the AutoFDO or AutoFDO+ThinLTO optimized + binary as you would normally do, but with a compile-time / + link-time flag to pick up the Propeller compile time and link time + profiles. This build step uses 3 profiles - the AutoFDO profile, + the Propeller compile-time profile and the Propeller link-time + profile. + +#. Deployment: The optimized kernel binary is deployed and used + in production environments, providing improved performance + and reduced latency. + +Preparation +=========== + +Configure the kernel with:: + + CONFIG_AUTOFDO_CLANG=y + CONFIG_PROPELLER_CLANG=y + +Customization +============= + +The default CONFIG_PROPELLER_CLANG setting covers kernel space objects +for Propeller builds. One can, however, enable or disable Propeller build +for individual files and directories by adding a line similar to the +following to the respective kernel Makefile: + +- For enabling a single file (e.g. foo.o):: + + PROPELLER_PROFILE_foo.o := y + +- For enabling all files in one directory:: + + PROPELLER_PROFILE := y + +- For disabling one file:: + + PROPELLER_PROFILE_foo.o := n + +- For disabling all files in one directory:: + + PROPELLER__PROFILE := n + + +Workflow +======== + +Here is an example workflow for building an AutoFDO+Propeller kernel: + +1) Assuming an AutoFDO profile is already collected following + instructions in the AutoFDO document, build the kernel on the host + machine, with AutoFDO and Propeller build configs :: + + CONFIG_AUTOFDO_CLANG=y + CONFIG_PROPELLER_CLANG=y + + and :: + + $ make LLVM=1 CLANG_AUTOFDO_PROFILE= + +2) Install the kernel on the test machine. + +3) Run the load tests. The '-c' option in perf specifies the sample + event period. We suggest using a suitable prime number, like 500009, + for this purpose. + + - For Intel platforms:: + + $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c -o -- + + - For AMD platforms:: + + $ perf record --pfm-event RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a -N -b -c -o -- + + Note you can repeat the above steps to collect multiple s. + +4) (Optional) Download the raw perf file(s) to the host machine. + +5) Use the create_llvm_prof tool (https://github.com/google/autofdo) to + generate Propeller profile. :: + + $ create_llvm_prof --binary= --profile= + --format=propeller --propeller_output_module_name + --out=_cc_profile.txt + --propeller_symorder=_ld_profile.txt + + "" can be something like "/home/user/dir/any_string". + + This command generates a pair of Propeller profiles: + "_cc_profile.txt" and + "_ld_profile.txt". + + If there are more than 1 perf_file collected in the previous step, + you can create a temp list file "" with each line + containing one perf file name and run:: + + $ create_llvm_prof --binary= --profile=@ + --format=propeller --propeller_output_module_name + --out=_cc_profile.txt + --propeller_symorder=_ld_profile.txt + +6) Rebuild the kernel using the AutoFDO and Propeller + profiles. :: + + CONFIG_AUTOFDO_CLANG=y + CONFIG_PROPELLER_CLANG=y + + and :: + + $ make LLVM=1 CLANG_AUTOFDO_PROFILE= CLANG_PROPELLER_PROFILE_PREFIX= diff --git a/MAINTAINERS b/MAINTAINERS index d6ea49433747a..42e3af0791e15 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -18449,6 +18449,13 @@ S: Maintained F: include/linux/psi* F: kernel/sched/psi.c +PROPELLER BUILD +M: Rong Xu +M: Han Shen +S: Supported +F: Documentation/dev-tools/propeller.rst +F: scripts/Makefile.propeller + PRINTK M: Petr Mladek R: Steven Rostedt diff --git a/Makefile b/Makefile index b89d87b5dca79..b2830b27e1a7f 100644 --- a/Makefile +++ b/Makefile @@ -1019,6 +1019,7 @@ include-$(CONFIG_UBSAN) += scripts/Makefile.ubsan include-$(CONFIG_KCOV) += scripts/Makefile.kcov include-$(CONFIG_RANDSTRUCT) += scripts/Makefile.randstruct include-$(CONFIG_AUTOFDO_CLANG) += scripts/Makefile.autofdo +include-$(CONFIG_PROPELLER_CLANG) += scripts/Makefile.propeller include-$(CONFIG_GCC_PLUGINS) += scripts/Makefile.gcc-plugins include $(addprefix $(srctree)/, $(include-y)) diff --git a/arch/Kconfig b/arch/Kconfig index 8dca3b5e6ef53..00551f340dbe3 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -831,6 +831,25 @@ config AUTOFDO_CLANG If unsure, say N. +config ARCH_SUPPORTS_PROPELLER_CLANG + bool + +config PROPELLER_CLANG + bool "Enable Clang's Propeller build" + depends on ARCH_SUPPORTS_PROPELLER_CLANG + depends on CC_IS_CLANG && CLANG_VERSION >= 190000 + help + This option enables Clang’s Propeller build. When the Propeller + profiles is specified in variable CLANG_PROPELLER_PROFILE_PREFIX + during the build process, Clang uses the profiles to optimize + the kernel. + + If no profile is specified, Propeller options are still passed + to Clang to facilitate the collection of perf data for creating + the Propeller profiles in subsequent builds. + + If unsure, say N. + config ARCH_SUPPORTS_CFI_CLANG bool help diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 9dc87661fb373..89b8fc452a7cf 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -127,6 +127,7 @@ config X86 select ARCH_SUPPORTS_LTO_CLANG_THIN select ARCH_SUPPORTS_RT select ARCH_SUPPORTS_AUTOFDO_CLANG + select ARCH_SUPPORTS_PROPELLER_CLANG if X86_64 select ARCH_USE_BUILTIN_BSWAP select ARCH_USE_CMPXCHG_LOCKREF if X86_CMPXCHG64 select ARCH_USE_MEMTEST diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index b8c5741d2fb48..cf22081601ed6 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -443,6 +443,10 @@ SECTIONS STABS_DEBUG DWARF_DEBUG +#ifdef CONFIG_PROPELLER_CLANG + .llvm_bb_addr_map : { *(.llvm_bb_addr_map) } +#endif + ELF_DETAILS DISCARDS diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 8a0bb3946cf05..c995474e4c649 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -95,14 +95,14 @@ * With LTO_CLANG, the linker also splits sections by default, so we need * these macros to combine the sections during the final link. * - * With AUTOFDO_CLANG, by default, the linker splits text sections and - * regroups functions into subsections. + * With AUTOFDO_CLANG and PROPELLER_CLANG, by default, the linker splits + * text sections and regroups functions into subsections. * * RODATA_MAIN is not used because existing code already defines .rodata.x * sections to be brought in with rodata. */ #if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) || \ -defined(CONFIG_AUTOFDO_CLANG) +defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG) #define TEXT_MAIN .text .text.[0-9a-zA-Z_]* #else #define TEXT_MAIN .text diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib index 2d0942c1a0277..e7859ad90224a 100644 --- a/scripts/Makefile.lib +++ b/scripts/Makefile.lib @@ -201,6 +201,16 @@ _c_flags += $(if $(patsubst n%,, \ $(CFLAGS_AUTOFDO_CLANG)) endif +# +# Enable Propeller build flags except some files or directories we don't want to +# enable (depends on variables AUTOFDO_PROPELLER_obj.o and PROPELLER_PROFILE). +# +ifdef CONFIG_PROPELLER_CLANG +_c_flags += $(if $(patsubst n%,, \ + $(AUTOFDO_PROFILE_$(target-stem).o)$(AUTOFDO_PROFILE)$(PROPELLER_PROFILE))$(is-kernel-object), \ + $(CFLAGS_PROPELLER_CLANG)) +endif + # $(src) for including checkin headers from generated source files # $(obj) for including generated headers from checkin source files ifeq ($(KBUILD_EXTMOD),) diff --git a/scripts/Makefile.propeller b/scripts/Makefile.propeller new file mode 100644 index 0000000000000..344190717e471 --- /dev/null +++ b/scripts/Makefile.propeller @@ -0,0 +1,28 @@ +# SPDX-License-Identifier: GPL-2.0 + +# Enable available and selected Clang Propeller features. +ifdef CLANG_PROPELLER_PROFILE_PREFIX + CFLAGS_PROPELLER_CLANG := -fbasic-block-sections=list=$(CLANG_PROPELLER_PROFILE_PREFIX)_cc_profile.txt -ffunction-sections + KBUILD_LDFLAGS += --symbol-ordering-file=$(CLANG_PROPELLER_PROFILE_PREFIX)_ld_profile.txt --no-warn-symbol-ordering +else + CFLAGS_PROPELLER_CLANG := -fbasic-block-sections=labels +endif + +# Propeller requires debug information to embed module names in the profiles. +# If CONFIG_DEBUG_INFO is not enabled, set -gmlt option. Skip this for AutoFDO, +# as the option should already be set. +ifndef CONFIG_DEBUG_INFO + ifndef CONFIG_AUTOFDO_CLANG + CFLAGS_PROPELLER_CLANG += -gmlt + endif +endif + +ifdef CONFIG_LTO_CLANG_THIN + ifdef CLANG_PROPELLER_PROFILE_PREFIX + KBUILD_LDFLAGS += --lto-basic-block-sections=$(CLANG_PROPELLER_PROFILE_PREFIX)_cc_profile.txt + else + KBUILD_LDFLAGS += --lto-basic-block-sections=labels + endif +endif + +export CFLAGS_PROPELLER_CLANG diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 4c5229991e1e0..05a0fb4a3d1a0 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -4558,6 +4558,7 @@ static int validate_ibt(struct objtool_file *file) !strcmp(sec->name, "__mcount_loc") || !strcmp(sec->name, ".kcfi_traps") || !strcmp(sec->name, ".llvm.call-graph-profile") || + !strcmp(sec->name, ".llvm_bb_addr_map") || strstr(sec->name, "__patchable_function_entries")) continue;