From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751391AbcEKGti (ORCPT ); Wed, 11 May 2016 02:49:38 -0400 Received: from merlin.infradead.org ([205.233.59.134]:59298 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751276AbcEKGth (ORCPT ); Wed, 11 May 2016 02:49:37 -0400 Date: Wed, 11 May 2016 08:49:29 +0200 From: Peter Zijlstra To: bsegall@google.com Cc: Xunlei Pang , linux-kernel@vger.kernel.org, Juri Lelli , Ingo Molnar , Steven Rostedt , pjt@google.com Subject: Re: [PATCH] sched/fair: Fix the wrong throttled clock time for cfs_rq_clock_task() Message-ID: <20160511064929.GC3193@twins.programming.kicks-ass.net> References: <1462885398-14724-1-git-send-email-xlpang@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Tue, May 10, 2016 at 11:19:44AM -0700, bsegall@google.com wrote: > Xunlei Pang writes: > > > Two minor fixes for cfs_rq_clock_task(). > > 1) If cfs_rq is currently being throttled, we need to subtract the cfs > > throttled clock time. > > > > 2) Make "throttled_clock_task_time" update SMP unrelated. Now UP cases > > need it as well. > > > > Signed-off-by: Xunlei Pang > > --- > > kernel/sched/fair.c | 4 +--- > > 1 file changed, 1 insertion(+), 3 deletions(-) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index 1708729e..fb80a12 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -3655,7 +3655,7 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg) > > static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq) > > { > > if (unlikely(cfs_rq->throttle_count)) > > - return cfs_rq->throttled_clock_task; > > + return cfs_rq->throttled_clock_task - cfs_rq->throttled_clock_task_time; > > > > return rq_clock_task(rq_of(cfs_rq)) - cfs_rq->throttled_clock_task_time; > > } The alternative is obviously to do the subtraction in tg_throttle_down(), were we set ->throttled_clock_task. > > @@ -3793,13 +3793,11 @@ static int tg_unthrottle_up(struct task_group *tg, void *data) > > struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)]; > > > > cfs_rq->throttle_count--; > > -#ifdef CONFIG_SMP > > if (!cfs_rq->throttle_count) { > > /* adjust cfs_rq_clock_task() */ > > cfs_rq->throttled_clock_task_time += rq_clock_task(rq) - > > cfs_rq->throttled_clock_task; > > } > > -#endif > > > > return 0; > > } > > [Cc: pjt@google.com] > > This looks reasonable to me (at least the first part; I'm not > certain why the CONFIG_SMP ifdef was put in place). 64660c864f46 ("sched: Prevent interactions with throttled entities") Introduced it, because at that time it was about updating shares, which is only present on SMP. Then: f1b17280efbd ("sched: Maintain runnable averages across throttled periods") Added the clock thing inside it, and: 82958366cfea ("sched: Replace update_shares weight distribution with per-entity computation") took out the shares update and left the clock update, resulting in the current code.