Re: [PATCH v7 7/7] Add Propeller configuration for kernel build

[Yonghong Song <yonghong.song@linux.dev>]

On 11/2/24 10:51 AM, 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@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>
> ---
>   Documentation/dev-tools/index.rst     |   1 +
>   Documentation/dev-tools/propeller.rst | 162 ++++++++++++++++++++++++++
>   MAINTAINERS                           |   7 ++
>   Makefile                              |   1 +
>   arch/Kconfig                          |  19 +++
>   arch/x86/Kconfig                      |   1 +
>   arch/x86/kernel/vmlinux.lds.S         |   4 +
>   include/asm-generic/vmlinux.lds.h     |   6 +-
>   scripts/Makefile.lib                  |  10 ++
>   scripts/Makefile.propeller            |  28 +++++
>   tools/objtool/check.c                 |   1 +
>   11 files changed, 237 insertions(+), 3 deletions(-)
>   create mode 100644 Documentation/dev-tools/propeller.rst
>   create mode 100644 scripts/Makefile.propeller
>
> diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst
> index 6945644f7008a..3c0ac08b27091 100644
> --- a/Documentation/dev-tools/index.rst
> +++ b/Documentation/dev-tools/index.rst
> @@ -35,6 +35,7 @@ Documentation/dev-tools/testing-overview.rst
>      checkuapi
>      gpio-sloppy-logic-analyzer
>      autofdo
> +   propeller
>   
>   
>   .. only::  subproject and html
> diff --git a/Documentation/dev-tools/propeller.rst b/Documentation/dev-tools/propeller.rst
> new file mode 100644
> index 0000000000000..92195958e3dbc
> --- /dev/null
> +++ b/Documentation/dev-tools/propeller.rst
> @@ -0,0 +1,162 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=====================================
> +Using Propeller with the Linux kernel
> +=====================================
> +
> +This enables Propeller build support for the kernel when using Clang
> +compiler. Propeller is a profile-guided optimization (PGO) method used
> +to optimize binary executables. Like AutoFDO, it utilizes hardware
> +sampling to gather information about the frequency of execution of
> +different code paths within a binary. Unlike AutoFDO, this information
> +is then used right before linking phase to optimize (among others)
> +block layout within and across functions.
> +
> +A few important notes about adopting Propeller optimization:
> +
> +#. Although it can be used as a standalone optimization step, it is
> +   strongly recommended to apply Propeller on top of AutoFDO,
> +   AutoFDO+ThinLTO or Instrument FDO. The rest of this document
> +   assumes this paradigm.
> +
> +#. Propeller uses another round of profiling on top of
> +   AutoFDO/AutoFDO+ThinLTO/iFDO. The whole build process involves
> +   "build-afdo - train-afdo - build-propeller - train-propeller -
> +   build-optimized".
> +
> +#. Propeller requires LLVM 19 release or later for Clang/Clang++
> +   and the linker(ld.lld).
> +
> +#. In addition to LLVM toolchain, Propeller requires a profiling
> +   conversion tool: https://github.com/google/autofdo with a release
> +   after v0.30.1: https://github.com/google/autofdo/releases/tag/v0.30.1.
> +
> +The Propeller optimization process involves the following steps:
> +
> +#. Initial building: Build the AutoFDO or AutoFDO+ThinLTO binary as
> +   you would normally do, but with a set of compile-time / link-time
> +   flags, so that a special metadata section is created within the
> +   kernel binary. The special section is only intend to be used by the
> +   profiling tool, it is not part of the runtime image, nor does it
> +   change kernel run time text sections.
> +
> +#. Profiling: The above kernel is then run with a representative
> +   workload to gather execution frequency data. This data is collected
> +   using hardware sampling, via perf. Propeller is most effective on
> +   platforms supporting advanced PMU features like LBR on Intel
> +   machines. This step is the same as profiling the kernel for AutoFDO
> +   (the exact perf parameters can be different).
> +
> +#. Propeller profile generation: Perf output file is converted to a
> +   pair of Propeller profiles via an offline tool.
> +
> +#. Optimized build: Build the AutoFDO or AutoFDO+ThinLTO optimized
> +   binary as you would normally do, but with a compile-time /
> +   link-time flag to pick up the Propeller compile time and link time
> +   profiles. This build step uses 3 profiles - the AutoFDO profile,
> +   the Propeller compile-time profile and the Propeller link-time
> +   profile.
> +
> +#. Deployment: The optimized kernel binary is deployed and used
> +   in production environments, providing improved performance
> +   and reduced latency.
> +
> +Preparation
> +===========
> +
> +Configure the kernel with::
> +
> +   CONFIG_AUTOFDO_CLANG=y
> +   CONFIG_PROPELLER_CLANG=y
> +
> +Customization
> +=============
> +
> +The default CONFIG_PROPELLER_CLANG setting covers kernel space objects
> +for Propeller builds. One can, however, enable or disable Propeller build
> +for individual files and directories by adding a line similar to the
> +following to the respective kernel Makefile:
> +
> +- For enabling a single file (e.g. foo.o)::
> +
> +   PROPELLER_PROFILE_foo.o := y
> +
> +- For enabling all files in one directory::
> +
> +   PROPELLER_PROFILE := y
> +
> +- For disabling one file::
> +
> +   PROPELLER_PROFILE_foo.o := n
> +
> +- For disabling all files in one directory::
> +
> +   PROPELLER__PROFILE := n
> +
> +
> +Workflow
> +========
> +
> +Here is an example workflow for building an AutoFDO+Propeller kernel:
> +
> +1) Assuming an AutoFDO profile is already collected following
> +   instructions in the AutoFDO document, build the kernel on the host
> +   machine, with AutoFDO and Propeller build configs ::
> +
> +      CONFIG_AUTOFDO_CLANG=y
> +      CONFIG_PROPELLER_CLANG=y
> +
> +   and ::
> +
> +      $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<autofdo-profile-name>
> +
> +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::
> +
> +      $ perf record --pfm-event RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a -N -b -c <count> -o <perf_file> -- <loadtest>
> +
> +   Note you can repeat the above steps to collect multiple <perf_file>s.
> +
> +4) (Optional) Download the raw perf file(s) to the host machine.
> +
> +5) Use the create_llvm_prof tool (https://github.com/google/autofdo) to
> +   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

Prevously I am using perf-6.8.5-0.hs1.hsx.el9.x86_64 and it works fine.
Now in my system, the perf is upgraded to 6.12.gadc218676eef

[root@twshared7248.15.atn5 ~]# perf --version
perf version 6.12.gadc218676eef

and create_llvm_prof does not work any more.

The command to collect sampling data:

# perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c 500009 -- stress --cpu 36 --io 36 --vm 36 --vm-bytes 128M --timeout 300s
stress: info: [536354] dispatching hogs: 36 cpu, 36 io, 36 vm, 0 hdd
stress: info: [536354] successful run completed in 300s
[ perf record: Woken up 2210 times to write data ]
[ perf record: Captured and wrote 562.529 MB perf.data (701971 samples) ]
# uname -r
6.11.1-0_fbk0_lto_rc19_612_gb572dfac1b39

The kernel is a 6.11 lto kernel.

I then run the following command:
$ cat ../run.sh
# perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c 500009 \
#       -- stress --cpu 36 --io 36 --vm 36 --vm-bytes 128M --timeout 300s
# good: perf-6.8.5-0.hs1.hsx.el9.x86_64

# <propeller_profile_prefix>: /tmp/propeller
./create_llvm_prof --binary=vmlinux-6.11.1-0_fbk0_lto_rc19_612_gb572dfac1b39 \
          --profile=perf.data \
          --format=propeller --propeller_output_module_name \
          --out=/tmp/propeller_cc_profile.txt \
          --propeller_symorder=/tmp/propeller_ld_profile.txt

$ ./run.sh
WARNING: Logging before InitGoogleLogging() is written to STDERR
I20241212 13:12:18.401772 463318 llvm_propeller_binary_content.cc:376] 'vmlinux-6.11.1-0_fbk0_lto_rc19_612_gb572dfac1b39' is PIE: 0
I20241212 13:12:18.403692 463318 llvm_propeller_binary_content.cc:380] 'vmlinux-6.11.1-0_fbk0_lto_rc19_612_gb572dfac1b39' is relocatable: 0
I20241212 13:12:18.404873 463318 llvm_propeller_binary_content.cc:388] Build Id found in 'vmlinux-6.11.1-0_fbk0_lto_rc19_612_gb572dfac1b39': eaacd5a14abc48cf832b3ad0fa6c64635ab569a8
I20241212 13:12:18.521499 463318 llvm_propeller_binary_content.cc:376] 'vmlinux-6.11.1-0_fbk0_lto_rc19_612_gb572dfac1b39' is PIE: 0
I20241212 13:12:18.521530 463318 llvm_propeller_binary_content.cc:380] 'vmlinux-6.11.1-0_fbk0_lto_rc19_612_gb572dfac1b39' is relocatable: 0
I20241212 13:12:18.521553 463318 llvm_propeller_binary_content.cc:388] Build Id found in 'vmlinux-6.11.1-0_fbk0_lto_rc19_612_gb572dfac1b39': eaacd5a14abc48cf832b3ad0fa6c64635ab569a8
I20241212 13:12:18.521611 463318 llvm_propeller_perf_lbr_aggregator.cc:51] Parsing [1/1] perf.data ...
[ERROR:/home/runner/work/autofdo/autofdo/third_party/perf_data_converter/src/quipper/perf_reader.cc:1386] Event size 132 after uint64_t alignment of the filename length is greater than event size 128 reported by perf for the buildid event of type 0
W20241212 13:12:18.521708 463318 llvm_propeller_perf_lbr_aggregator.cc:55] Skipped profile [1/1] perf.data: FAILED_PRECONDITION: Failed to read perf data file: [1/1] perf.data
W20241212 13:12:18.521718 463318 llvm_propeller_perf_lbr_aggregator.cc:67] Too few branch records in perf data.
E20241212 13:12:18.554437 463318 create_llvm_prof.cc:238] FAILED_PRECONDITION: No perf file is parsed, cannot proceed.


Could you help take a look why perf 12 does not work with create_llvm_prof?
The create_llvm_prof is downloaded from https://github.com/google/autofdo/releases/tag/v0.30.1.

> +
> +   "<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".
> +
> +   If there are more than 1 perf_file collected in the previous step,
> +   you can create a temp list file "<perf_file_list>" with each line
> +   containing one perf file name and run::
> +
> +      $ create_llvm_prof --binary=<vmlinux> --profile=@<perf_file_list>
> +                         --format=propeller --propeller_output_module_name
> +                         --out=<propeller_profile_prefix>_cc_profile.txt
> +                         --propeller_symorder=<propeller_profile_prefix>_ld_profile.txt
> +
> +6) Rebuild the kernel using the AutoFDO and Propeller
> +   profiles. ::
> +
> +      CONFIG_AUTOFDO_CLANG=y
> +      CONFIG_PROPELLER_CLANG=y
> +
> +   and ::
> +
> +      $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file> CLANG_PROPELLER_PROFILE_PREFIX=<propeller_profile_prefix>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index d6ea49433747a..42e3af0791e15 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -18449,6 +18449,13 @@ S:	Maintained
>   F:	include/linux/psi*
>   F:	kernel/sched/psi.c
>
[...]