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SubjectRe: [PATCH] sched: Remove WAKEUP_PREEMPT feature check in entity_tick
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On Fri, 2011-07-29 at 15:46 +0800, Yong Zhang wrote:
> On Fri, Jul 29, 2011 at 03:36:15PM +0800, Lin Ming wrote:
> > >From another point of view, below !sched_feat(WAKEUP_PREEMPT) still
> > looks like duplicated.
> >
> > if (cfs_rq->nr_running > 1 || !sched_feat(WAKEUP_PREEMPT))
> > check_preempt_tick(cfs_rq, curr);
> >
> > if "!sched_feat(WAKEUP_PREEMPT)" is run,
> > that implies cfs_rq->nr_running == 1.
>
> That's true.
>
> >
> > Why do we need to call check_preempt_tick when there is only 1 task
> > runnable?
>
> Just set_tsk_need_resched(p) if p's slice is over, thus:
>
> (n tick) ---> (n+1 tick)
> set_tsk_need_resched(p);
> another task Q is awaked
>
> If we don't have !sched_feat(WAKEUP_PREEMPT), Q maybe will wait
> for tick coming to get scheduled. If we have
> !sched_feat(WAKEUP_PREEMPT), Q will get scheduled when some event
> happen, like IRQ.

Wow. That's really clear explanation.
Got it now.

Thanks!

>
> Thanks,
> Yong
>




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