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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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