From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933008AbcE3Jhu (ORCPT ); Mon, 30 May 2016 05:37:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52572 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932219AbcE3Jhs (ORCPT ); Mon, 30 May 2016 05:37:48 -0400 Reply-To: xlpang@redhat.com Subject: Re: [PATCH] sched/fair: Fix the wrong throttled clock time for cfs_rq_clock_task() References: <1462885398-14724-1-git-send-email-xlpang@redhat.com> <20160511064929.GC3193@twins.programming.kicks-ass.net> <5733FA51.4050509@redhat.com> To: Peter Zijlstra , bsegall@google.com Cc: Xunlei Pang , linux-kernel@vger.kernel.org, Juri Lelli , Ingo Molnar , Steven Rostedt , pjt@google.com From: Xunlei Pang Message-ID: <574C09E5.7050902@redhat.com> Date: Mon, 30 May 2016 17:37:41 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <5733FA51.4050509@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Mon, 30 May 2016 09:37:48 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ping On 2016/05/12 at 11:36, Xunlei Pang wrote: > On 2016/05/11 at 14:49, Peter Zijlstra wrote: >> 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. > It is possible, but throttled_clock_task is a timestamp, I think doing it here is semantically better. > >>>> @@ -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. >> >> > Thanks, > Xunlei >