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Date: Fri, 29 Jul 2011 15:36:15 +0800 From: Lin Ming <ming.m.lin@...el.com> To: Yong Zhang <yong.zhang0@...il.com> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>, "mingo@...e.hu" <mingo@...e.hu>, lkml <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] sched: Remove WAKEUP_PREEMPT feature check in entity_tick On Fri, 2011-07-29 at 15:03 +0800, Yong Zhang wrote: > On Fri, Jul 29, 2011 at 02:49:40PM +0800, Lin Ming wrote: > > On Fri, 2011-07-29 at 14:21 +0800, Yong Zhang wrote: > > > On Thu, Jul 28, 2011 at 05:43:23PM +0800, Lin Ming wrote: > > > > Currently, entity_tick calls check_preempt_tick if WAKEUP_PREEMPT feature is > > > > disabled. That's wrong. It should do that if the feature is enabled. > > > > > > Why is it wrong? > > > check_preempt_wakeup() is used for wakeup. > > > > I guess you mean "check_preempt_tick" here, yes? > > check_preempt_wakeup() excactly. > try_to_wake_up() > check_preempt_curr() > sched_fair->check_preempt_wakeup() <========== [1] > > > > > in entity_tick(...): > > if (cfs_rq->nr_running > 1 || !sched_feat(WAKEUP_PREEMPT)) > > check_preempt_tick(cfs_rq, curr); > > > > Note that, above "if" statement says "if WAKEUP_PREEMPT feature is > > *disabled* then calls check_preempt_tick". > > Yeah, if !sched_feat(WAKEUP_PREEMPT) [1] will just return; > thus new waked task will wait until the next tick to schedule. > > > > > Shouldn't it be "if WAKEUP_PREEMPT feature is *enabled* then ...."? > > So no IMHO. > > > > > > > > > > > > > > And actually the check is duplicate because check_preempt_tick will do > > > > that. So just remove it from entity_tick. > > > > > > It's not exactly duplicated. entity_tick() will resched_task(*p) > > > if p's slice is over. So if there is an following wakeup(say X), > > > then there is an opportunity for X to schedule quickly. > > > > Understood this. > > > > But what I mean is both "entity_tick" and "check_preempt_tick" check > > WAKEUP_PREEMPT feature. That's duplicated. > > > > Only need to check it in "check_preempt_tick". > > I think we need that check(!sched_feat(WAKEUP_PREEMPT)) in entity_tick() > to give new waked task better opportunity. Thanks for your explanation. >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. Why do we need to call check_preempt_tick when there is only 1 task runnable? Thanks, Lin Ming -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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