On Fri, Oct 25, 2024 at 10:14:09PM -0700, Rong Xu 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 > 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@xxxxxxxxxx> > Signed-off-by: Han Shen <shenhan@xxxxxxxxxx> Looks good. Similarly isolated like FDO. :) Reviewed-by: Kees Cook <kees@xxxxxxxxxx> -- Kees Cook
