Re: [PATCH v7 1/7] Add AutoFDO support for Clang build

[Han Shen <shenhan@google.com>]

Hi Peter, thanks for reporting the issue. I am trying to reproduce it
in the up-to-date archlinux environment. Below is what I have:
  0. pacman -Syu
  1. cloned archlinux build files from
https://aur.archlinux.org/linux-mainline.git the newest mainline
version is 6.12rc5-1.
  2. changed the PKGBUILD file to include the patches series
  3. changed the "config" to turn on clang autofdo
  4. collected afdo profiles
  5. MAKEFLAGS="-j48 V=1 LLVM=1 CLANG_AUTOFDO_PROFILE=$(pwd)/perf.afdo" \
        makepkg -s --skipinteg --skippgp
  6. install and reboot
The above steps succeeded.
You mentioned the error happens at "module_install", can you instruct
me how to execute the "module_install" step?

Thanks,
Han

On Sat, Nov 2, 2024 at 12:53 PM Peter Jung <ptr1337@cachyos.org> wrote:
>
>
>
> On 02.11.24 20:46, Peter Jung wrote:
> >
> >
> > On 02.11.24 18:51, 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@google.com>
> >> Signed-off-by: Han Shen<shenhan@google.com>
> >> Signed-off-by: Rong Xu<xur@google.com>
> >> Suggested-by: Sriraman Tallam<tmsriram@google.com>
> >> Suggested-by: Krzysztof Pszeniczny<kpszeniczny@google.com>
> >> Suggested-by: Nick Desaulniers<ndesaulniers@google.com>
> >> Suggested-by: Stephane Eranian<eranian@google.com>
> >> Tested-by: Yonghong Song<yonghong.song@linux.dev>
> >> Tested-by: Yabin Cui<yabinc@google.com>
> >> Tested-by: Nathan Chancellor<nathan@kernel.org>
> >> Reviewed-by: Kees Cook<kees@kernel.org>
> >
> > Tested-by: Peter Jung <ptr1337@cachyos.org>
> >
>
> The compilations and testing with the "make pacman-pkg" function from
> the kernel worked fine.
>
> One problem I do face:
> When I apply a AutoFDO profile together with the PKGBUILD [1] from
> archlinux im running into issues at "module_install" at the packaging.
>
> See following log:
> ```
> make[2]: *** [scripts/Makefile.modinst:125:
> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/arch/x86/kvm/kvm.ko]
> Error 1
> make[2]: *** Deleting file
> '/tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/arch/x86/kvm/kvm.ko'
>    INSTALL
> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/crypto/cryptd.ko
> make[2]: *** Waiting for unfinished jobs....
> ```
>
>
> This can be fixed with removed "INSTALL_MOD_STRIP=1" to the passed
> parameters of module_install.
>
> This explicitly only happens, if a profile is passed - otherwise the
> packaging works without problems.
>
> Regards,
>
> Peter Jung
>