From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S943238AbcJSOuD (ORCPT ); Wed, 19 Oct 2016 10:50:03 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:45736 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S943016AbcJSOuA (ORCPT ); Wed, 19 Oct 2016 10:50:00 -0400 Subject: Re: [v4.8-rc1 Regression] sched/fair: Apply more PELT fixes To: Vincent Guittot , Peter Zijlstra References: <20161014151827.GA10379@linaro.org> <2bb765e7-8a5f-c525-a6ae-fbec6fae6354@canonical.com> <20161017090903.GA11962@linaro.org> <4e15ad55-beeb-e860-0420-8f439d076758@arm.com> <20161017131952.GR3117@twins.programming.kicks-ass.net> <94cc6deb-f93e-60ec-5834-e84a8b98e73c@arm.com> <20161018090747.GW3142@twins.programming.kicks-ass.net> <20161018103412.GT3117@twins.programming.kicks-ass.net> <20161018115651.GA20956@linaro.org> Cc: Dietmar Eggemann , Ingo Molnar , Linus Torvalds , Thomas Gleixner , LKML , Mike Galbraith , omer.akram@canonical.com From: Joseph Salisbury Message-ID: <8b29f878-29bc-8efa-6d34-d5df3b68e020@canonical.com> Date: Wed, 19 Oct 2016 10:49:56 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: <20161018115651.GA20956@linaro.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/18/2016 07:56 AM, Vincent Guittot wrote: > Le Tuesday 18 Oct 2016 à 12:34:12 (+0200), Peter Zijlstra a écrit : >> On Tue, Oct 18, 2016 at 11:45:48AM +0200, Vincent Guittot wrote: >>> On 18 October 2016 at 11:07, Peter Zijlstra wrote: >>>> So aside from funny BIOSes, this should also show up when creating >>>> cgroups when you have offlined a few CPUs, which is far more common I'd >>>> think. >>> The problem is also that the load of the tg->se[cpu] that represents >>> the tg->cfs_rq[cpu] is initialized to 1024 in: >>> alloc_fair_sched_group >>> for_each_possible_cpu(i) { >>> init_entity_runnable_average(se); >>> sa->load_avg = scale_load_down(se->load.weight); >>> >>> Initializing sa->load_avg to 1024 for a newly created task makes >>> sense as we don't know yet what will be its real load but i'm not sure >>> that we have to do the same for se that represents a task group. This >>> load should be initialized to 0 and it will increase when task will be >>> moved/attached into task group >> Yes, I think that makes sense, not sure how horrible that is with the > That should not be that bad because this initial value is only useful for > the few dozens of ms that follow the creation of the task group > >> current state of things, but after your propagate patch, that >> reinstates the interactivity hack that should work for sure. > The patch below fixes the issue on my platform: > > Dietmar, Omer can you confirm that this fix the problem of your platform too ? > > --- > kernel/sched/fair.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-)Vinc > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 8b03fb5..89776ac 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -690,7 +690,14 @@ void init_entity_runnable_average(struct sched_entity *se) > * will definitely be update (after enqueue). > */ > sa->period_contrib = 1023; > - sa->load_avg = scale_load_down(se->load.weight); > + /* > + * Tasks are intialized with full load to be seen as heavy task until > + * they get a chance to stabilize to their real load level. > + * group entity are intialized with null load to reflect the fact that > + * nothing has been attached yet to the task group. > + */ > + if (entity_is_task(se)) > + sa->load_avg = scale_load_down(se->load.weight); > sa->load_sum = sa->load_avg * LOAD_AVG_MAX; > /* > * At this point, util_avg won't be used in select_task_rq_fair anyway > > > > Omer also reports that this patch fixes the bug for him as well. Thanks for the great work, Vincent!