linux-kernel - Re: [PATCH v6 1/7] Add AutoFDO support for Clang build

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <202410281708.83F316FF@keescook>
Date: Mon, 28 Oct 2024 17:08:44 -0700
From: Kees Cook <kees@...nel.org>
To: Rong Xu <xur@...gle.com>
Cc: 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>,
	David Li <davidxl@...gle.com>, Han Shen <shenhan@...gle.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>,
	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>,
	Peter Zijlstra <peterz@...radead.org>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Wei Yang <richard.weiyang@...il.com>, workflows@...r.kernel.org,
	Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
	Maksim Panchenko <max4bolt@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Andreas Larsson <andreas@...sler.com>,
	Yonghong Song <yonghong.song@...ux.dev>,
	Yabin Cui <yabinc@...gle.com>,
	Krzysztof Pszeniczny <kpszeniczny@...gle.com>,
	Sriraman Tallam <tmsriram@...gle.com>,
	Stephane Eranian <eranian@...gle.com>, x86@...nel.org,
	linux-arch@...r.kernel.org, sparclinux@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v6 1/7] Add AutoFDO support for Clang build

On Fri, Oct 25, 2024 at 10:14:03PM -0700, Rong Xu wrote:
> 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 <count> \
>         -o <perf_file> -- <loadtest>
>    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 <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 or
>    later, or from the LLVM trunk.
>       $ llvm-profgen --kernel --binary=<vmlinux> --perfdata=<perf_file> \
>         -o <profile_file>
>    or
>       $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
>         --format=extbinary --out=<profile_file>
> 
>    Note that multiple AutoFDO profile files can be merged into one via:
>       $ llvm-profdata merge -o <profile_file>  <profile_1> ... <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):
>       $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>
> 
> Co-developed-by: Han Shen <shenhan@...gle.com>
> Signed-off-by: Han Shen <shenhan@...gle.com>

This looks good. Fairly well isolated.

Reviewed-by: Kees Cook <kees@...nel.org>

-- 
Kees Cook