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Message-ID: <20241003154143.GW5594@noisy.programming.kicks-ass.net>
Date: Thu, 3 Oct 2024 17:41:43 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Rong Xu <xur@...gle.com>
Cc: Han Shen <shenhan@...gle.com>, Sriraman Tallam <tmsriram@...gle.com>,
David Li <davidxl@...gle.com>,
Krzysztof Pszeniczny <kpszeniczny@...gle.com>,
Alice Ryhl <aliceryhl@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Arnd Bergmann <arnd@...db.de>, Bill Wendling <morbo@...gle.com>,
Borislav Petkov <bp@...en8.de>, Breno Leitao <leitao@...ian.org>,
Brian Gerst <brgerst@...il.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Heiko Carstens <hca@...ux.ibm.com>,
"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Juergen Gross <jgross@...e.com>,
Justin Stitt <justinstitt@...gle.com>, Kees Cook <kees@...nel.org>,
linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
llvm@...ts.linux.dev, Masahiro Yamada <masahiroy@...nel.org>,
"Mike Rapoport (IBM)" <rppt@...nel.org>,
Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Nicolas Schier <nicolas@...sle.eu>,
"Paul E. McKenney" <paulmck@...nel.org>,
Samuel Holland <samuel.holland@...ive.com>,
Thomas Gleixner <tglx@...utronix.de>,
Wei Yang <richard.weiyang@...il.com>, workflows@...r.kernel.org,
x86@...nel.org, "Xin Li (Intel)" <xin@...or.com>,
Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v2 1/6] Add AutoFDO support for Clang build
On Wed, Oct 02, 2024 at 04:34:00PM -0700, Rong Xu wrote:
> +Preparation
> +===========
> +
> +Configure the kernel with:
> +
> + .. code-block:: make
> +
> + CONFIG_AUTOFDO_CLANG=y
> +
> +Customization
> +=============
> +
> +You can enable or disable AutoFDO build for individual file and directories by
> +adding a line similar to the following to the respective kernel Makefile:
> +
> +- For enabling a single file (e.g. foo.o)
> +
> + .. code-block:: make
> +
> + AUTOFDO_PROFILE_foo.o := y
> +
> +- For enabling all files in one directory
> +
> + .. code-block:: make
> +
> + AUTOFDO_PROFILE := y
> +
> +- For disabling one file
> +
> + .. code-block:: make
> +
> + AUTOFDO_PROFILE_foo.o := n
> +
> +- For disabling all files in one directory
> +
> + .. code-block:: make
> +
> + 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,
> +
> + .. code-block:: make
> +
> + $ make menuconfig LLVM=1
> +
> +
> + Turn on AutoFDO build config:
> +
> + .. code-block:: make
> +
> + CONFIG_AUTOFDO_CLANG=y
> +
> + With a configuration that with LLVM enabled, use the following command:
> +
> + .. code-block:: sh
> +
> + $ scripts/config -e AUTOFDO_CLANG
> +
> + After getting the config, build with
> +
> + .. code-block:: make
> +
> + $ 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:
> +
> + .. code-block:: sh
> +
> + $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c <count> -o <perf_file> -- <loadtest>
> +
> + - For AMD platforms: For Intel platforms:
> + The supported systems are: Zen3 with BRS, or Zen4 with amd_lbr_v2. To check,
> + For Zen3:
> +
> + .. code-block:: sh
> +
> + $ cat proc/cpuinfo | grep " brs"
> +
> + For Zen4:
> +
> + .. code-block:: sh
> +
> + $ cat proc/cpuinfo | grep amd_lbr_v2
> +
> + The following command generated the perf data file:
> +
> + .. code-block:: sh
> +
> + $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a -N -b \
> + -c <count> -o <perf_file> -- <loadtest>
> +
> +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.
> +
> + .. code-block:: sh
> +
> + $ llvm-profgen --kernel --binary=<vmlinux> --perfdata=<perf_file> -o <profile_file>
> +
> + or
> + .. code-block:: sh
> +
> + $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> --format=extbinary -o <profile_file>
> +
> + Note that multiple AutoFDO profile files can be merged into one via:
> +
> + .. code-block:: sh
> +
> + $ llvm-profdata merge -o <profile_file> <profile_1> <profile_2> ... <profile_n>
> +
> +
> +6) Rebuild the kernel using the AutoFDO profile file with the same config as step 1,
> + (Note CONFIG_AUTOFDO_CLANG needs to be enabled):
> +
> + .. code-block:: sh
> +
> + $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file
> +
Can this be done without the endless ... code-block nonsense?
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