From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Yong Zhang <yong.zhang0@gmail.com>
Cc: Lin Ming <ming.m.lin@intel.com>, "mingo@elte.hu" <mingo@elte.hu>,
lkml <linux-kernel@vger.kernel.org>,
Mike Galbraith <efault@gmx.de>
Subject: Re: [PATCH] sched: Remove WAKEUP_PREEMPT feature check in entity_tick
Date: Fri, 29 Jul 2011 13:45:33 +0200 [thread overview]
Message-ID: <1311939933.5890.341.camel@twins> (raw)
In-Reply-To: <20110729084637.GC12106@zhy>
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 ;-)
next prev parent reply other threads:[~2011-07-29 11:46 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-28 9:43 [PATCH] sched: Remove WAKEUP_PREEMPT feature check in entity_tick Lin Ming
2011-07-29 6:21 ` Yong Zhang
2011-07-29 6:24 ` Yong Zhang
2011-07-29 6:49 ` Lin Ming
2011-07-29 7:03 ` Yong Zhang
2011-07-29 7:36 ` Lin Ming
2011-07-29 7:46 ` Yong Zhang
2011-07-29 7:56 ` Lin Ming
2011-07-29 7:56 ` Peter Zijlstra
2011-07-29 8:18 ` Yong Zhang
2011-07-29 8:20 ` Peter Zijlstra
2011-07-29 8:44 ` Lin Ming
2011-07-29 8:46 ` Yong Zhang
2011-07-29 11:45 ` Peter Zijlstra [this message]
2011-08-01 1:33 ` Yong Zhang
2011-07-29 8:20 ` [RFC PATCH] sched: Kill WAKEUP_PREEMPT Yong Zhang
2011-07-29 8:30 ` Lin Ming
2011-07-29 8:32 ` Lin Ming
2011-08-14 15:57 ` [tip:sched/core] " tip-bot for Yong Zhang
2011-07-29 9:04 ` [PATCH] sched: Remove WAKEUP_PREEMPT feature check in entity_tick Mike Galbraith
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