Re: [PATCH -tip] x86/locking/atomic: Use asm_inline for atomic locking insns

Uros Bizjak
2025-03-05T08:54:19Z

On Sat, Mar 1, 2025 at 1:38 PM Borislav Petkov <bp@alien8.de> wrote:
>
> On Sat, Mar 01, 2025 at 10:05:56AM +0100, Uros Bizjak wrote:
> > OTOH, -Os, where different code size/performance heuristics are used, now
> > performs better w.r.t code size.
>
> Did anything change since:
>
> 281dc5c5ec0f ("Give up on pushing CC_OPTIMIZE_FOR_SIZE")
> 3a55fb0d9fe8 ("Tell the world we gave up on pushing CC_OPTIMIZE_FOR_SIZE")
>
> wrt -Os?
>
> Because if not, we still don't love -Os and you can drop the -Os argument.

The -Os argument was to show the effect of the patch when the compiler
is instructed to take care of the overall size. Giving the compiler
-O2 and then looking at the overall size of the produced binary is
just wrong.

> And without any perf data showing any improvement, this patch does nothing but
> enlarge -O2 size...

Even to my surprise, the patch has some noticeable effects on the
performance, please see the attachment in [1] for LMBench data or [2]
for some excerpts from the data. So, I think the patch has potential
to improve the performance.

[1] https://lore.kernel.org/lkml/CAFULd4YBcG45bigHBox2pu+To+Y5BzbRxG+pUr42AVOWSnfKsg@mail.gmail.com/
[2] https://lore.kernel.org/lkml/CAFULd4ZsSKwJ4Dz3cCAgaVsa4ypbb0e2savO-3_Ltbs=1wzgKQ@mail.gmail.com/

Thanks,
Uros.