Re: [PATCH v2] kbuild: rust: add AutoFDO support

Nathan Chancellor
2026-04-07T16:45:32Z

On Fri, Apr 03, 2026 at 07:02:15AM +0200, Miguel Ojeda wrote:
> On Tue, Mar 31, 2026 at 12:58 PM Alice Ryhl <aliceryhl@google.com> wrote:
> >
> > This patch enables AutoFDO build support for Rust code within the Linux
> > kernel. This allows Rust code to be profiled and optimized based on the
> > profile.
> >
> > The RUSTFLAGS variable was suffixed with *_AUTOFDO_CLANG to match the
> > naming of the config option, which is called CONFIG_AUTOFDO_CLANG.
> >
> > This implementation has been verified in Android, first by inspecting
> > the object files and confirming that they look correct. After that,
> > it was verified as below:
> >
> > 1. Running the binderAddInts benchmark [1] with Rust Binder built as
> > rust_binder.ko module, using a Pixel 9 Pro.
> > 2. Collecting a profile on an Pixel 10 Pro XL using the app-launch
> > benchmark, which starts different apps many times, on a device with
> > Rust Binder as a built-in kernel module. (C Binder was not present on
> > the device.)
> > 3. Using the collected profile, run the binderAddInts benchmark again
> > with Rust Binder built both as a rust_binder.ko module, and as a
> > built-in kernel module.
> > 4. In both cases, Rust Binder without AutoFDO was approximately 13%
> > slower than the AutoFDO optimized version. Built-in vs .ko did not
> > make a measurable performance difference.
> >
> > All of the above was verified in conjuction with my helpers inlining
> > series [2], which confirmed that this worked correctly for helpers too
> > once [3] was fixed in the helpers inlining series.
> >
> > Link: https://android.googlesource.com/platform/system/extras/+/920f089/tests/binder/benchmarks/binderAddInts.cpp [1]
> > Link: https://lore.kernel.org/r/20260203-inline-helpers-v2-0-beb8547a03c9@google.com [2]
> > Link: https://lore.kernel.org/r/aasPsbMEsX6iGUl8@google.com [3]
> > Reviewed-by: Rong Xu <xur@google.com>
> > Reviewed-by: Gary Guo <gary@garyguo.net>
> > Tested-by: Alice Ryhl <aliceryhl@google.com>
> > Signed-off-by: Alice Ryhl <aliceryhl@google.com>
>
> If Rong/Han or Kbuild want to pick this up, then:
>
> Acked-by: Miguel Ojeda <ojeda@kernel.org>
>
> Otherwise, please let me know -- thanks!

Unless Nicolas feels strongly otherwise, I think you can just take this
via the Rust tree.

Acked-by: Nathan Chancellor <nathan@kernel.org>

Cheers,
Nathan