Re: [PATCH v4 1/6] Add AutoFDO support for Clang build

[Rong Xu <xur@google.com>]

Thanks for the detailed suggestions! My comments are inlined below.

Best regards,

-Rong

On Sun, Oct 20, 2024 at 9:33 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Tue, Oct 15, 2024 at 6:33 AM Rong Xu <xur@google.com> wrote:
>
>
> > +Customization
> > +=============
> > +
> > +You can enable or disable AutoFDO build for individual file and directories by
> > +adding a line similar to the following to the respective kernel Makefile:
>
>
> Perhaps, it might be worth mentioning that kernel space objects are
> covered by default.
>
> Then, people would understand ':= y' will be less common than ':= n'.
>

Good point! How about I change to the following:
"
The default CONFIG_AUTOFDO_CLANG setting covers kernel space objects for
AutoFDO builds. One can, however, enable or disable AutoFDO build for
individual file and directories by adding a line similar to the following
to the respective kernel Makefile ...

>
>
>
> > +
> > +- For enabling a single file (e.g. foo.o) ::
> > +
> > +   AUTOFDO_PROFILE_foo.o := y
> > +
> > +- For enabling all files in one directory ::
> > +
> > +   AUTOFDO_PROFILE := y
> > +
> > +- For disabling one file ::
> > +
> > +   AUTOFDO_PROFILE_foo.o := n
> > +
> > +- For disabling all files in one directory ::
> > +
> > +   AUTOFDO_PROFILE := n
> > +
>
>
>
>
> > +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: For Intel platforms:
>
>
> I guess this is a copy-paste mistake.
>
>
> For AMD platforms: For Intel platforms:
>
>    ->
>
> For AMD platforms:

Thanks for catching this! Will fix this.

>
>
>
>
>
>
> > +   (https://github.com/google/autofdo),  version v0.30.1 or later.
>
>
> Please one space instead of two after the comma.
>

Will fix it.

>
>
>
>
>
>
> > diff --git a/scripts/Makefile.autofdo b/scripts/Makefile.autofdo
> > new file mode 100644
> > index 000000000000..1c9f224bc221
> > --- /dev/null
> > +++ b/scripts/Makefile.autofdo
> > @@ -0,0 +1,23 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +
> > +# Enable available and selected Clang AutoFDO features.
> > +
> > +CFLAGS_AUTOFDO_CLANG := -fdebug-info-for-profiling -mllvm -enable-fs-discriminator=true -mllvm -improved-fs-discriminator=true
> > +
> > +# If CONFIG_DEBUG_INFO is not enabled, set -gmlt option.
>
>
> Meaningless comment. It explains too obvious code.

Will remove this line of comment.

>
>
> > +ifndef CONFIG_DEBUG_INFO
> > +  CFLAGS_AUTOFDO_CLANG += -gmlt
> > +endif
>
>
>
>
> > diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> > index 01a9f567d5af..e85d6ac31bd9 100644
> > --- a/scripts/Makefile.lib
> > +++ b/scripts/Makefile.lib
> > @@ -191,6 +191,16 @@ _c_flags += $(if $(patsubst n%,, \
> >         -D__KCSAN_INSTRUMENT_BARRIERS__)
> >  endif
> >
> > +#
> > +# Enable Clang's AutoFDO build flags for a file or directory depending on
> > +# variables AUTOFDO_PROFILE_obj.o and AUTOFDO_PROFILE.
> > +#
>
>
> This comment would give the wrong understanding that this flag is opt-in.
>
>
> The comment for KASAN correctly describes that it is enabled by default,
> and can be opted out using KASAN_SANITIZE_*.
>

I can change to use KASAN's expression:
"
# Enable Clang's AutoFDO build flags for kernel except some files or directories
# we don't want to enable (depends on variables AUTOFDO_PROFILE_obj.o
and AUTOFDO_PROFILE)
"

>
>
>
>
> --
> Best Regards
>
>
> Masahiro Yamada