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Date: Mon, 1 Aug 2011 09:33:41 +0800 From: Yong Zhang <yong.zhang0@...il.com> To: Peter Zijlstra <a.p.zijlstra@...llo.nl> Cc: Lin Ming <ming.m.lin@...el.com>, "mingo@...e.hu" <mingo@...e.hu>, lkml <linux-kernel@...r.kernel.org>, Mike Galbraith <efault@....de> Subject: Re: [PATCH] sched: Remove WAKEUP_PREEMPT feature check in entity_tick On Fri, Jul 29, 2011 at 01:45:33PM +0200, Peter Zijlstra wrote: > On Fri, 2011-07-29 at 16:46 +0800, Yong Zhang wrote: > > Let's take UP for example, we have cpu-hug task A and threadirq B. > > > > n tick ---> n+1 tick > > set_tsk_need_resched(A); > > B comes in and > > wake up thread-B; > > > > So for system on which we disable WAKEUP_PREEMPT, > > if we don't have that check, thread-B will wait until n+1 tick comes > > to get to run. > > But if we have that check, thread-B will get to run after IRQ-B returns. > > But that's exactly what wakeup preemption is about, waking tasks don't > get to preempt running tasks. So no doing that preemption is exactly > right for !WAKEUP_PREEMPT. > > Anyway, I've queued the removal patch since that removes all > confusion ;-) Yup, that sounds good. Thanks Peter. -Yong -- Only stand for myself -- 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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