Re: [RFC v2 3/7] Improve the tracking of active utilisation

luca abeni
2016-04-05T17:05:27Z

Hi Peter,

On Tue, 5 Apr 2016 14:42:42 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> On Fri, Apr 01, 2016 at 05:12:29PM +0200, Luca Abeni wrote:
> > @@ -526,7 +575,18 @@ static void update_dl_entity(struct sched_dl_entity *dl_se,
> > struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
> > struct rq *rq = rq_of_dl_rq(dl_rq);
> >
> > - add_running_bw(dl_se, dl_rq);
> > + /*
> > + * If the "inactive timer" is still active, stop it and leave
> > + * the active utilisation unchanged.
> > + * Otherwise, increase the active utilisation.
> > + * If the timer cannot be cancelled, inactive_task_timer() will
> > + * find the task state as TASK_RUNNING, and will do nothing, so
> > + * we are still safe.
> > + */
> > + if (hrtimer_active(&dl_se->inactive_timer))
> > + hrtimer_try_to_cancel(&dl_se->inactive_timer);
>
> _try_, what happens if that fails?

I think inactive_task_timer() will run, but will see p->state == TASK_RUNNING
and will return immediately.

I think I have actually seen this happening during my tests, because adding
the "if (p->state == TASK_RUNNING)" in inactive_task_timer() fixed some issues
that I was seeing.

Thanks,
Luca