From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755384Ab1G2ISL (ORCPT ); Fri, 29 Jul 2011 04:18:11 -0400 Received: from mail-vw0-f46.google.com ([209.85.212.46]:42927 "EHLO mail-vw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754590Ab1G2ISJ (ORCPT ); Fri, 29 Jul 2011 04:18:09 -0400 Date: Fri, 29 Jul 2011 16:18:00 +0800 From: Yong Zhang To: Peter Zijlstra Cc: Lin Ming , "mingo@elte.hu" , lkml , Mike Galbraith Subject: Re: [PATCH] sched: Remove WAKEUP_PREEMPT feature check in entity_tick Message-ID: <20110729081800.GA12106@zhy> Reply-To: Yong Zhang References: <1311846203.3938.1555.camel@minggr.sh.intel.com> <20110729062158.GA8971@zhy> <1311922180.3938.1573.camel@minggr.sh.intel.com> <20110729070356.GA10420@zhy> <1311924975.3938.1583.camel@minggr.sh.intel.com> <20110729074635.GB10420@zhy> <1311926218.5890.215.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1311926218.5890.215.camel@twins> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 29, 2011 at 09:56:58AM +0200, Peter Zijlstra wrote: > 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. Hmmm, so the newly waked task could be scheduled a little later. That means schedule tick judge everything. Thanks, Yong > > 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.. > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- Only stand for myself