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From: Yafang Shao <laoar.shao@gmail.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Daniel Drake <drake@endlessm.com>,
	Suren Baghdasaryan <surenb@google.com>
Subject: Re: [PATCH] psi: fix randomized calculation in record_times()
Date: Sat, 4 Apr 2020 10:31:16 +0800	[thread overview]
Message-ID: <CALOAHbBqk4s4Nw3Ky3YY66EM7DzUJZTuLZhjw9+ULUE-9O+aDQ@mail.gmail.com> (raw)
In-Reply-To: <20200403152016.GA69203@cmpxchg.org>

On Fri, Apr 3, 2020 at 11:20 PM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> On Fri, Apr 03, 2020 at 04:55:25AM -0400, Yafang Shao wrote:
> > @@ -690,7 +690,10 @@ static void psi_group_change(struct psi_group *group, int cpu,
> >        */
> >       write_seqcount_begin(&groupc->seq);
> >
> > -     record_times(groupc, cpu, false);
> > +     if (groupc->total_tasks)
> > +             record_times(groupc, cpu, false);
> > +     else
> > +             groupc->state_start = cpu_clock(cpu);
>
> This change appears is a no-op. If there are no tasks,
> groupc->state_mask is 0, and the only thing record_times() does is
>
>         groupc->state_start = cpu_clock(cpu);
>
> Did you encounter actual problems, or are you just reading the code?

No real issues. Just reading the code and found it looks like a little weird.
But as you explained that state_mask can also guarantee it then we
don't need to make this change.

Thanks for the explanation.

Thanks
Yafang

      reply	other threads:[~2020-04-04  2:31 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-03  8:55 [PATCH] psi: fix randomized calculation in record_times() Yafang Shao
2020-04-03 15:20 ` Johannes Weiner
2020-04-04  2:31   ` Yafang Shao [this message]

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