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SubjectRe: [PATCH 06/16] sched: SCHED_DEADLINE push and pull logic
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On Tue, 2012-04-24 at 15:15 +0200, Peter Zijlstra wrote:
> On Wed, 2012-04-11 at 12:33 -0400, Steven Rostedt wrote:
> > On Fri, 2012-04-06 at 09:14 +0200, Juri Lelli wrote:
> > >
> > > @@ -543,6 +897,9 @@ static void put_prev_task_dl(struct rq *rq, struct task_struct *p)
> > > {
> > > update_curr_dl(rq);
> > > p->se.exec_start = 0;
> > > +
> > > + if (on_dl_rq(&p->dl) && p->dl.nr_cpus_allowed > 1)
> > > + enqueue_pushable_dl_task(rq, p);
> > > }
> >
> > Ouch! We need to fix this. This has nothing to do with your patch
> > series, but if you look at schedule():
> >
> > put_prev_task(rq, prev);
> > next = pick_next_task(rq);
> >
> >
> > We put the prev task and then pick the next task. If we call schedule
> > for some reason when we don't need to really schedule, then we just
> > added and removed from the pushable rb tree the same task. That is, we
> > did the rb manipulation twice, for no good reason.
> >
> > Not sure how to fix this. But it will require a generic change.
>
>
> Something like so: https://lkml.org/lkml/2012/2/16/487 ?

But it still does the same thing:

+static struct task_struct *
+pick_next_task_rt(struct rq *rq, struct task_struct *prev)
{
- struct task_struct *p = _pick_next_task_rt(rq);
+ struct task_struct *p;
+ struct rt_rq *rt_rq = &rq->rt;
+
+ if (!rt_rq->rt_nr_running)
+ return NULL;
+
+ if (rt_rq_throttled(rt_rq))
+ return NULL;
+
+ if (prev)
+ prev->sched_class->put_prev_task(rq, prev);
+
+ p = _pick_next_task_rt(rq);
Now if we can do the _pick_next_task_rt() before put_prev_task(), and
only do the put_prev_task() if p != prev, then that would be something.

-- Steve




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