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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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