Hi Han,
I have tested your provided method, but the AutoFDO profile (lld does
not get lto-sample-profile=$pathtoprofile passed) nor Clang as compiler
gets used.
Please replace following PKGBUILD and config from linux-mainline with
the provided one in the gist. The patch is also included there.
https://gist.github.com/ptr1337/c92728bb273f7dbc2817db75eedec9ed
The main change I am doing here, is passing following to the build array
and replacing "make all":
make LLVM=1 LLVM_IAS=1 CLANG_AUTOFDO_PROFILE=${srcdir}/perf.afdo all
When compiling the kernel with makepkg, this results at the packaging to
following issue and can be reliable reproduced.
Regards,
Peter
On 04.11.24 05:50, Han Shen wrote:
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@xxxxxxxxxxx> 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@xxxxxxxxxx>
Signed-off-by: Han Shen<shenhan@xxxxxxxxxx>
Signed-off-by: Rong Xu<xur@xxxxxxxxxx>
Suggested-by: Sriraman Tallam<tmsriram@xxxxxxxxxx>
Suggested-by: Krzysztof Pszeniczny<kpszeniczny@xxxxxxxxxx>
Suggested-by: Nick Desaulniers<ndesaulniers@xxxxxxxxxx>
Suggested-by: Stephane Eranian<eranian@xxxxxxxxxx>
Tested-by: Yonghong Song<yonghong.song@xxxxxxxxx>
Tested-by: Yabin Cui<yabinc@xxxxxxxxxx>
Tested-by: Nathan Chancellor<nathan@xxxxxxxxxx>
Reviewed-by: Kees Cook<kees@xxxxxxxxxx>
Tested-by: Peter Jung<ptr1337@xxxxxxxxxxx>
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
