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d5dc958361
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> |
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