From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751921AbbASMpm (ORCPT ); Mon, 19 Jan 2015 07:45:42 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:52194 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750728AbbASMpl (ORCPT ); Mon, 19 Jan 2015 07:45:41 -0500 Date: Mon, 19 Jan 2015 13:45:28 +0100 From: Peter Zijlstra To: Wanpeng Li Cc: Ingo Molnar , Juri Lelli , Kirill Tkhai , linux-kernel@vger.kernel.org, tim.c.chen@linux.intel.com, riel@redhat.com, jason.low2@hp.com, fweisbec@gmail.com Subject: Re: [PATCH v6 5/7] sched/fair: fix idle balance when remaining tasks are all non-CFS tasks Message-ID: <20150119124528.GO25256@twins.programming.kicks-ass.net> References: <1416962647-76792-1-git-send-email-wanpeng.li@linux.intel.com> <1416962647-76792-6-git-send-email-wanpeng.li@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1416962647-76792-6-git-send-email-wanpeng.li@linux.intel.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 26, 2014 at 08:44:05AM +0800, Wanpeng Li wrote: > The overload indicator is used for knowing when we can totally avoid load > balancing to a cpu that is about to go idle. We can avoid load balancing > when no cpu has cfs task and both rt and deadline have push/pull mechanism > to do their own balancing. > > However, rq->nr_running on behalf of the total number of each class tasks > on the cpu, do idle balance when remaining tasks are all non-CFS tasks does > not make any sense. > > This patch fix it by idle balance when there are still other CFS tasks in > the rq's root domain. > Please always try and Cc the people who touched that code last; for the idle_balance bits commit 4486edd12b5a ("sched/fair: Implement fast idling of CPUs when the system is partially loaded") gives a fair clue as to who that would be. > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 31f1e4d..f7dd978 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1269,7 +1269,8 @@ static inline void add_nr_running(struct rq *rq, unsigned count) > > rq->nr_running = prev_nr + count; > > - if (prev_nr < 2 && rq->nr_running >= 2) { > + if (prev_nr < 2 && rq->nr_running >= 2 && > + rq->cfs.h_nr_running > 0) { > #ifdef CONFIG_SMP > if (!rq->rd->overload) > rq->rd->overload = true; Here 3882ec643997 ("nohz: Use IPI implicit full barrier against rq->nr_running r/w") might be a clue. Also, this is wrong, it breaks NOHZ_FULL.