Re: [PATCH] sched: Remove WAKEUP_PREEMPT feature check in entity_tick

[Yong Zhang]

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.

Thanks,
Yong

-- 
Only stand for myself
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