linux-kernel - Re: [PATCH] kexec: Use atomic_try_cmpxchg_acquire() in kexec

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Message-ID: <Zp40zOw+E1Na/Lly@MiWiFi-R3L-srv>
Date: Mon, 22 Jul 2024 18:30:36 +0800
From: Baoquan He <bhe@...hat.com>
To: Uros Bizjak <ubizjak@...il.com>
Cc: akpm@...ux-foundation.org, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Eric Biederman <ebiederm@...ssion.com>
Subject: Re: [PATCH] kexec: Use atomic_try_cmpxchg_acquire() in
 kexec_trylock()

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

Good to know, thanks for telling.