Re: [PATCH 6/6] Add Propeller configuration for kernel build.

[Masahiro Yamada]

On Mon, Jul 29, 2024 at 5:31 AM Rong Xu <xur@xxxxxxxxxx> 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
> submission is limited to x86 platforms that support PMU features
> like LBR on Intel machines and AMD Zen3 BRS.
>
> For Arm, we plan to send patches for SPE-based Propeller when
> AutoFDO for Arm is ready.
>
> 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>
> 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>
> ---





> diff --git a/Makefile b/Makefile
> index 5ae30cc94a26..85a96d973f20 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1025,6 +1025,7 @@ include-$(CONFIG_KCOV)            += scripts/Makefile.kcov
>  include-$(CONFIG_RANDSTRUCT)   += scripts/Makefile.randstruct
>  include-$(CONFIG_GCC_PLUGINS)  += scripts/Makefile.gcc-plugins
>  include-$(CONFIG_AUTOFDO_CLANG)        += scripts/Makefile.autofdo
> +include-$(CONFIG_PROPELLER_CLANG)      += scripts/Makefile.propeller



Please do not ignore this comment:

https://github.com/torvalds/linux/blob/v6.11/Makefile#L1016







> +ifdef CONFIG_LTO_CLANG
> +ifdef CONFIG_LTO_CLANG_THIN
> +ifdef CLANG_PROPELLER_PROFILE_PREFIX
> +KBUILD_LDFLAGS += --lto-basic-block-sections=$(CLANG_PROPELLER_PROFILE_PREFIX)_cc_profile.txt
> +else
> +KBUILD_LDFLAGS += --lto-basic-block-sections=labels
> +endif
> +endif
> +else
> +endif


Unreadable and redundant.


ifdef CONFIG_LTO_CLANG_THIN
  ifdef CLANG_PROPELLER_PROFILE_PREFIX
    KBUILD_LDFLAGS +=
--lto-basic-block-sections=$(CLANG_PROPELLER_PROFILE_PREFIX)_cc_profile.txt
  else
    KBUILD_LDFLAGS += --lto-basic-block-sections=labels
  endif
endif










-- 
Best Regards
Masahiro Yamada