linux-kernel - Re: [PATCH v3 5/5] psi: introduce psi monitor

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Message-ID: <CAJuCfpH3k0rrZZw_HhrjXYuFX31p283qg_5vQEnyd_wAMaxbqA@mail.gmail.com>
Date:   Tue, 29 Jan 2019 10:05:07 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tejun Heo <tj@...nel.org>, lizefan@...wei.com,
        Johannes Weiner <hannes@...xchg.org>, axboe@...nel.dk,
        dennis@...nel.org, Dennis Zhou <dennisszhou@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>, cgroups@...r.kernel.org,
        linux-mm <linux-mm@...ck.org>, linux-doc@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, kernel-team@...roid.com
Subject: Re: [PATCH v3 5/5] psi: introduce psi monitor

Thanks for review Peter!

On Tue, Jan 29, 2019 at 2:44 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Thu, Jan 24, 2019 at 01:15:18PM -0800, Suren Baghdasaryan wrote:
> >  static void psi_update_work(struct work_struct *work)
> >  {
> >       struct delayed_work *dwork;
> >       struct psi_group *group;
> > +     bool first_pass = true;
> > +     u64 next_update;
> > +     u32 change_mask;
> > +     int polling;
> >       bool nonidle;
> > +     u64 now;
> >
> >       dwork = to_delayed_work(work);
> >       group = container_of(dwork, struct psi_group, clock_work);
> >
> > +     now = sched_clock();
> > +
> > +     mutex_lock(&group->update_lock);
>
> actually acquiring a mutex can take a fairly long while; would it not
> make more sense to take the @now timestanp _after_ it, instead of
> before?

Yes, that makes sense. As long as *now* is set before the *retry*
label, otherwise the retry mechanism would get even more complicated
to understand with floating *now* timestamp. Will move the assignment
right after the mutex_lock()

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