Re: [PATCH v3 5/5] psi: introduce psi monitor

[Suren Baghdasaryan]

Thanks for review Peter!

On Tue, Jan 29, 2019 at 2:44 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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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