[PATCH] kexec: Use atomic_try_cmpxchg_acquire() in kexec_trylock()

[Uros Bizjak]

On Mon, Jul 22, 2024 at 5:09 AM Baoquan He <bhe at redhat.com> wrote:
>
> On 07/19/24 at 12:38pm, Uros Bizjak wrote:
> > Use atomic_try_cmpxchg_acquire(*ptr, &old, new) instead of
> > atomic_cmpxchg_acquire(*ptr, old, new) == old in kexec_trylock().
> > x86 CMPXCHG instruction returns success in ZF flag, so
> > this change saves a compare after cmpxchg.
>
> Seems it can simplify code even though on non-x86 arch, should we
> replace atomic_try_cmpxchg_acquire() with atomic_try_cmpxchg_acquire()
> in all similar places?

Yes, the change is beneficial also for non-x86 architectures, please
see analysis at thread [1]. I've been looking through the kernel
sources for these places for quite some time, and I believe I have
changed most of the places. The change is relatively straightforward,
and immediately results in a better code.

[1] https://lore.kernel.org/lkml/871qwgmqws.fsf@mpe.ellerman.id.au/

>
> For this one,
>
> Acked-by: Baoquan He <bhe at redhat.com>

Thanks,
Uros.