Re: [RFCv5 PATCH 11/46] sched: Remove blocked load and utilization contributions of dying tasks

Morten Rasmussen
2015-08-11T14:55:46Z

On Tue, Aug 11, 2015 at 01:39:27PM +0200, Peter Zijlstra wrote:
> On Tue, Jul 07, 2015 at 07:23:54PM +0100, Morten Rasmussen wrote:
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 775b0c7..fa12ce5 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3217,6 +3217,8 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
> > * Update run-time statistics of the 'current'.
> > */
> > update_curr(cfs_rq);
> > + if (entity_is_task(se) && task_of(se)->state == TASK_DEAD)
> > + flags &= !DEQUEUE_SLEEP;
> > dequeue_entity_load_avg(cfs_rq, se, flags & DEQUEUE_SLEEP);
> >
> > update_stats_dequeue(cfs_rq, se);
>
> I know this is entirely redundant at this point (we took Yuyang's
> patches), but this is the wrong way to go about doing this.

Yes, I'm still working my way through Yuyang's changes.

> You add extra code the hot dequeue path for something that 'never'
> happens. We have the sched_class::task_dead call for that.

I don't mind using sched_class::task_dead() instead. The reason why I
didn't go that way is that we have to retake the rq->lock or mess with
cfs_rq::removed_load instead of just not adding the utilization in
the first place when we have the rq->lock.

Anyway, it is probably redundant by now. I will check Yuyang's code to
see if he already fixed this problem.