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From: Suren Baghdasaryan <surenb@google.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Johannes Weiner" <hannes@cmpxchg.org>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Juri Lelli" <juri.lelli@redhat.com>,
	"Vincent Guittot" <vincent.guittot@linaro.org>,
	"Dietmar Eggemann" <dietmar.eggemann@arm.com>,
	"Steven Rostedt" <rostedt@goodmis.org>,
	"Benjamin Segall" <bsegall@google.com>,
	"Mel Gorman" <mgorman@suse.de>,
	"Daniel Bristot de Oliveira" <bristot@redhat.com>,
	matthias.bgg@gmail.com, "Minchan Kim" <minchan@google.com>,
	"Tim Murray" <timmurray@google.com>,
	"YT Chang" <yt.chang@mediatek.com>,
	"Wenju Xu (许文举)" <wenju.xu@mediatek.com>,
	"Jonathan JMChen (陳家明)" <jonathan.jmchen@mediatek.com>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org,
	kernel-team <kernel-team@android.com>,
	"SH Chen" <show-hong.chen@mediatek.com>
Subject: Re: [PATCH v2 1/1] psi: stop relying on timer_pending for poll_work rescheduling
Date: Thu, 1 Jul 2021 09:28:04 -0700	[thread overview]
Message-ID: <CAJuCfpFKDhcgjU=MGsz+JuetrWvYCe0EL3FMp91zopH+8T=mMQ@mail.gmail.com> (raw)
In-Reply-To: <YN3pUNgpBjn42f8s@hirez.programming.kicks-ass.net>

On Thu, Jul 1, 2021 at 9:12 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Thu, Jul 01, 2021 at 09:09:25AM -0700, Suren Baghdasaryan wrote:
> > On Thu, Jul 1, 2021 at 1:59 AM Peter Zijlstra <peterz@infradead.org> wrote:
> > >
> > > On Wed, Jun 30, 2021 at 01:51:51PM -0700, Suren Baghdasaryan wrote:
> > > > +     /* cmpxchg should be called even when !force to set poll_scheduled */
> > > > +     if (atomic_cmpxchg(&group->poll_scheduled, 0, 1) && !force)
> > > >               return;
> > >
> > > Why is that a cmpxchg() ?
> >
> > We want to set poll_scheduled and proceed with rescheduling the timer
> > unless it's already scheduled, so cmpxchg helps us to make that
> > decision atomically. Or did I misunderstand your question?
>
> What's wrong with: atomic_xchg(&group->poll_scheduled, 1) ?

Yes, since poll_scheduled can be only 0 or 1 atomic_xchg should work
fine here. Functionally equivalent but I assume atomic_xchg() is more
efficient due to no comparison.
Will respin v3 if the rest looks ok.

>
> --
> To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com.
>

  reply	other threads:[~2021-07-01 16:28 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-30 20:51 [PATCH v2 1/1] psi: stop relying on timer_pending for poll_work rescheduling Suren Baghdasaryan
2021-06-30 22:04 ` Johannes Weiner
2021-07-01  8:58 ` Peter Zijlstra
2021-07-01 16:09   ` Suren Baghdasaryan
2021-07-01 16:12     ` Peter Zijlstra
2021-07-01 16:28       ` Suren Baghdasaryan [this message]
2021-07-02  9:28         ` Peter Zijlstra
2021-07-02 15:49           ` Suren Baghdasaryan
2021-07-07  2:42             ` Suren Baghdasaryan
2021-07-01 16:39   ` Johannes Weiner
2021-07-01 17:46     ` Suren Baghdasaryan

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