Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936173AbXHIIgX (ORCPT ); Thu, 9 Aug 2007 04:36:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754435AbXHIIgM (ORCPT ); Thu, 9 Aug 2007 04:36:12 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:36291 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752219AbXHIIgL (ORCPT ); Thu, 9 Aug 2007 04:36:11 -0400 Date: Thu, 9 Aug 2007 10:36:06 +0200 From: Ingo Molnar To: Dmitry Adamushko Cc: Mitchell Erblich , Linux Kernel Mailing List Subject: Re: Question: RT schedular : task_tick_rt(struct rq *rq, struct task_struct *p) : decreases overhead when rq->nr_running == 1 Message-ID: <20070809083606.GA24130@elte.hu> References: <000501c7d945$f30af1a0$6501a8c0@earthlink.net> <20070808123418.GA30248@elte.hu> <20070809082656.GA21973@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070809082656.GA21973@elte.hu> User-Agent: Mutt/1.5.14 (2007-02-12) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.0.3 -1.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1609 Lines: 53 FYI, that's the patch i applied: ---------------------------> Subject: sched: optimize task_tick_rt() a bit From: Dmitry Adamushko Mitchell Erblich suggested a change to not requeue SCHED_RR tasks if there's only a single task on the runqueue, by checking for rq->nr_running == 1. provide a more efficient implementation of that, to check that particular RT priority-queue only. [ From: mingo@elte.hu ] Also first requeue the task then set need_resched - results in slightly better machine-instruction ordering. Also clean up the code a bit. Signed-off-by: Ingo Molnar --- kernel/sched_rt.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) Index: linux/kernel/sched_rt.c =================================================================== --- linux.orig/kernel/sched_rt.c +++ linux/kernel/sched_rt.c @@ -207,10 +207,15 @@ static void task_tick_rt(struct rq *rq, return; p->time_slice = static_prio_timeslice(p->static_prio); - set_tsk_need_resched(p); - /* put it at the end of the queue: */ - requeue_task_rt(rq, p); + /* + * Requeue to the end of queue if we are not the only element + * on the queue: + */ + if (p->run_list.prev != p->run_list.next) { + requeue_task_rt(rq, p); + set_tsk_need_resched(p); + } } static struct sched_class rt_sched_class __read_mostly = { - 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/