linux-kernel - Re: [PATCH] arm64: Allow CONFIG_AUTOFDO

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Message-ID: <CAF1bQ=R=481iZu1Zp8p42zvGd_oLrU-K9UHtSe9TbZUDkS8Qkw@mail.gmail.com>
Date: Thu, 14 Nov 2024 23:02:35 -0800
From: Rong Xu <xur@...gle.com>
To: Yabin Cui <yabinc@...gle.com>
Cc: Han Shen <shenhan@...gle.com>, Jonathan Corbet <corbet@....net>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
	Masahiro Yamada <masahiroy@...nel.org>, Kees Cook <kees@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, workflows@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: Allow CONFIG_AUTOFDO_CLANG to be selected

Hi Yabin,

Thanks for working to enable this on ARM64 and test the performance on Android!
Please see my comments below.

Thanks,

-Rong

On Thu, Nov 14, 2024 at 9:11 PM Yabin Cui <yabinc@...gle.com> wrote:
>
> Select ARCH_SUPPORTS_AUTOFDO_CLANG to allow AUTOFDO_CLANG to be
> selected.
>
> On ARM64, ETM traces can be recorded and converted to AutoFDO profiles.
> Experiments on Android show 4% improvement in cold app startup time
> and 13% improvement in binder benchmarks.
>
> Signed-off-by: Yabin Cui <yabinc@...gle.com>
> ---
>  Documentation/dev-tools/autofdo.rst | 18 +++++++++++++++++-
>  arch/arm64/Kconfig                  |  1 +
>  2 files changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/dev-tools/autofdo.rst b/Documentation/dev-tools/autofdo.rst
> index 1f0a451e9ccd..f0952e3e8490 100644
> --- a/Documentation/dev-tools/autofdo.rst
> +++ b/Documentation/dev-tools/autofdo.rst
> @@ -55,7 +55,7 @@ process consists of the following steps:
>     workload to gather execution frequency data. This data is
>     collected using hardware sampling, via perf. AutoFDO is most
>     effective on platforms supporting advanced PMU features like
> -   LBR on Intel machines.
> +   LBR on Intel machines, ETM traces on ARM machines.
>
>  #. AutoFDO profile generation: Perf output file is converted to
>     the AutoFDO profile via offline tools.
> @@ -141,6 +141,22 @@ Here is an example workflow for AutoFDO kernel:
>
>        $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a -N -b -c <count> -o <perf_file> -- <loadtest>
>
> +   - For ARM platforms:

The instructions for SPE might be different. Can we change to "- For
ARM platforms with ETM trace:"

> +
> +     Follow the instructions in the `Linaro OpenCSD document
> +     https://github.com/Linaro/OpenCSD/blob/master/decoder/tests/auto-fdo/autofdo.md`_
> +     to record ETM traces for AutoFDO::
> +
> +      $ perf record -e cs_etm/@..._etr0/k -a -o <etm_perf_file> -- <loadtest>
> +      $ perf inject -i <etm_perf_file> -o <perf_file> --itrace=i500009il
> +
> +     For ARM platforms running Android, follow the instructions in the
> +     `Android simpleperf document
> +     <https://android.googlesource.com/platform/system/extras/+/main/simpleperf/doc/collect_etm_data_for_autofdo.md>`_
> +     to record ETM traces for AutoFDO::

The instructions in "Step 3: Convert ETM data to AutoFDO profile"
currently use create_llvm_prof to generate
 a "binary" profile format. This is incompatible with the default
FSAFDO format used for the kernel, which
 requires an "extbinary" format.

To correct this, please update the instructions to include the flag
"-format extbinary" in the
create_llvm_prof command.

Using a non-FSAFDO profile with FSAFDO can negatively impact performance.
Therefore, I recommend rerunning the test with the updated flag to
potentially achieve better results.

> +
> +      $ simpleperf record -e cs-etm:k -a -o <perf_file> -- <loadtest>
> +
>  4) (Optional) Download the raw perf file to the host machine.
>
>  5) To generate an AutoFDO profile, two offline tools are available:
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index fd9df6dcc593..c3814df5e391 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -103,6 +103,7 @@ config ARM64
>         select ARCH_SUPPORTS_PER_VMA_LOCK
>         select ARCH_SUPPORTS_HUGE_PFNMAP if TRANSPARENT_HUGEPAGE
>         select ARCH_SUPPORTS_RT
> +       select ARCH_SUPPORTS_AUTOFDO_CLANG
>         select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
>         select ARCH_WANT_COMPAT_IPC_PARSE_VERSION if COMPAT
>         select ARCH_WANT_DEFAULT_BPF_JIT
> --
> 2.47.0.338.g60cca15819-goog
>