linux-kernel - Re: [PATCH 6/6] Add Propeller configuration for kernel build.

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Message-ID: <CAK7LNAQ0Z38a1Nt=_XKT3i-UpauiO9RaZAye6LXGCFzvg2R8Bg@mail.gmail.com>
Date: Sun, 29 Sep 2024 20:08:43 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Rong Xu <xur@...gle.com>
Cc: Han Shen <shenhan@...gle.com>, Sriraman Tallam <tmsriram@...gle.com>, 
	David Li <davidxl@...gle.com>, Jonathan Corbet <corbet@....net>, 
	Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H . Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
	Josh Poimboeuf <jpoimboe@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, Vegard Nossum <vegard.nossum@...cle.com>, 
	John Moon <john@...on.dev>, Andrew Morton <akpm@...ux-foundation.org>, 
	Heiko Carstens <hca@...ux.ibm.com>, Luis Chamberlain <mcgrof@...nel.org>, 
	Samuel Holland <samuel.holland@...ive.com>, Mike Rapoport <rppt@...nel.org>, 
	"Paul E . McKenney" <paulmck@...nel.org>, Rafael Aquini <aquini@...hat.com>, Petr Pavlu <petr.pavlu@...e.com>, 
	Eric DeVolder <eric.devolder@...cle.com>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Randy Dunlap <rdunlap@...radead.org>, Benjamin Segall <bsegall@...gle.com>, 
	Breno Leitao <leitao@...ian.org>, Wei Yang <richard.weiyang@...il.com>, 
	Brian Gerst <brgerst@...il.com>, Juergen Gross <jgross@...e.com>, 
	Palmer Dabbelt <palmer@...osinc.com>, Alexandre Ghiti <alexghiti@...osinc.com>, 
	Kees Cook <kees@...nel.org>, Sami Tolvanen <samitolvanen@...gle.com>, 
	Xiao Wang <xiao.w.wang@...el.com>, Jan Kiszka <jan.kiszka@...mens.com>, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-kbuild@...r.kernel.org, linux-efi@...r.kernel.org, 
	linux-arch@...r.kernel.org, llvm@...ts.linux.dev, 
	Krzysztof Pszeniczny <kpszeniczny@...gle.com>, Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 6/6] Add Propeller configuration for kernel build.

On Mon, Jul 29, 2024 at 5:31 AM Rong Xu <xur@...gle.com> wrote:
>
> 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
> submission is limited to x86 platforms that support PMU features
> like LBR on Intel machines and AMD Zen3 BRS.
>
> For Arm, we plan to send patches for SPE-based Propeller when
> AutoFDO for Arm is ready.
>
> 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=<autofdo_profile>
>
> “<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 <count> \
>         -o <perf_file> -- <loadtest>
>    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 <count> -o <perf_file> -- <loadtest>
>
> 4) (Optional) Download the raw perf file to the HOST machine.
>
> 5) Generate Propeller profile:
>    $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
>      --format=propeller --propeller_output_module_name \
>      --out=<propeller_profile_prefix>_cc_profile.txt \
>      --propeller_symorder=<propeller_profile_prefix>_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).
>
>    "<propeller_profile_prefix>" can be something like
>    "/home/user/dir/any_string".
>
>    This command generates a pair of Propeller profiles:
>    "<propeller_profile_prefix>_cc_profile.txt" and
>    "<propeller_profile_prefix>_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=<autofdo_profile> \
>         CLANG_PROPELLER_PROFILE_PREFIX=<propeller_profile_prefix>
>
> Co-developed-by: Han Shen <shenhan@...gle.com>
> Signed-off-by: Han Shen <shenhan@...gle.com>
> Signed-off-by: Rong Xu <xur@...gle.com>
> Suggested-by: Sriraman Tallam <tmsriram@...gle.com>
> Suggested-by: Krzysztof Pszeniczny <kpszeniczny@...gle.com>
> Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Suggested-by: Stephane Eranian <eranian@...gle.com>
> ---





> diff --git a/Makefile b/Makefile
> index 5ae30cc94a26..85a96d973f20 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1025,6 +1025,7 @@ include-$(CONFIG_KCOV)            += scripts/Makefile.kcov
>  include-$(CONFIG_RANDSTRUCT)   += scripts/Makefile.randstruct
>  include-$(CONFIG_GCC_PLUGINS)  += scripts/Makefile.gcc-plugins
>  include-$(CONFIG_AUTOFDO_CLANG)        += scripts/Makefile.autofdo
> +include-$(CONFIG_PROPELLER_CLANG)      += scripts/Makefile.propeller



Please do not ignore this comment:

https://github.com/torvalds/linux/blob/v6.11/Makefile#L1016







> +ifdef CONFIG_LTO_CLANG
> +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
> +else
> +endif


Unreadable and redundant.


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










-- 
Best Regards
Masahiro Yamada