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
commit is limited to x86 platforms that support PMU features
like LBR on Intel machines and AMD Zen3 BRS.
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@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: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
d5dc958361