Messages in this thread | | | Subject | Re: [PATCH] sched: Remove WAKEUP_PREEMPT feature check in entity_tick | From | Peter Zijlstra <> | Date | Fri, 29 Jul 2011 09:56:58 +0200 |
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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.
Nah, if there is 1 runnable task it will always run, preemption simply doesn't matter. There's nothing to preempt it with.
I've queued Lin's patch as I don't see the point of this thing either, normally WAKEUP_PREEMPT is enabled so it says || 0 which is kinda useless :-)
And I'm starting to think we should just kill all of WAKEUP_PREEMPT I don't think we ever want to disable it anyway..
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