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

[Baoquan He]

On 07/22/24 at 10:53am, Uros Bizjak wrote:
> On Mon, Jul 22, 2024 at 5:09 AM Baoquan He <bhe@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx/

Good to know, thanks for telling.