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SubjectRe: [RFC 0/12][PATCH] SCHED_DEADLINE: core of the scheduling class
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On Tue, 2009-12-29 at 15:37 +0100, Peter Zijlstra wrote:
> On Tue, 2009-12-29 at 15:30 +0100, Peter Zijlstra wrote:
> > On Fri, 2009-10-16 at 17:40 +0200, Raistlin wrote:
> > > +struct task_struct *pick_next_task_deadline(struct rq *rq)
> > > +{
> > > + struct sched_dl_entity *dl_se;
> > > + struct task_struct *p;
> > > + struct dl_rq *dl_rq;
> > > +
> > > + dl_rq = &rq->dl;
> > > +
> > > + if (likely(!dl_rq->dl_nr_running))
> > > + return NULL;
> > > +
> > > + dl_se = pick_next_deadline_entity(rq, dl_rq);
> > > + BUG_ON(!dl_se);
> > > +
> > > + p = deadline_task_of(dl_se);
> > > + p->se.exec_start = rq->clock;
> > > +#ifdef CONFIG_SCHED_HRTICK
> > > + if (hrtick_enabled(rq))
> > > + start_hrtick_deadline(rq, p);
> > > +#endif
> > > + return p;
> > > +}
> >
> > I'm not sure about actually using hrtick like this, I'd expect
> > SCHED_DEADLINE to always use hrtimers when available. The only reason
> > to use some of the hrtick infrastructure is to re-use the hrtick_start()
> > logic which uses IPIs to ensure we program the timer on the right cpu
> > (so we can schedule from it).
>
> Hmm I suppose we could ignore all that CONFIG_SCHED_HRTICK stuff and
> simply bounce the schedule event using the resched ipi when we find
> we're on the wrong cpu. Not ideal though.. frigging mess all this :-)

Hmm bugger that, that's not going to work since the fallback timer stuff
doesn't run from hardirq context and is generally useless anyway :-)



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