linux-kernel - Re: [PATCH] sched/clock: Use try_cmpxchg64 in sched_clock

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Message-ID: <20220519074752.GC2578@worktop.programming.kicks-ass.net>
Date:   Thu, 19 May 2022 09:47:52 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Uros Bizjak <ubizjak@...il.com>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH] sched/clock: Use try_cmpxchg64 in
 sched_clock_{local,remote}

On Wed, May 18, 2022 at 08:49:53PM +0200, Uros Bizjak wrote:
> Use try_cmpxchg64 instead of cmpxchg64 (*ptr, old, new) != old in
> sched_clock_{local,remote}. x86 cmpxchg returns success in ZF flag,
> so this change saves a compare after cmpxchg (and related move
> instruction in front of cmpxchg).
> 
> Signed-off-by: Uros Bizjak <ubizjak@...il.com>

Thanks!