From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754971AbcFQKJk (ORCPT ); Fri, 17 Jun 2016 06:09:40 -0400 Received: from mga09.intel.com ([134.134.136.24]:21847 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751301AbcFQKJi (ORCPT ); Fri, 17 Jun 2016 06:09:38 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.26,483,1459839600"; d="scan'208";a="830002834" Date: Fri, 17 Jun 2016 10:12:51 +0800 From: Yuyang Du To: Vincent Guittot Cc: Peter Zijlstra , Ingo Molnar , linux-kernel , Mike Galbraith , Benjamin Segall , Paul Turner , Morten Rasmussen , Dietmar Eggemann , Matt Fleming Subject: Re: [PATCH v6 1/4] sched/fair: Fix attaching task sched avgs twice when switching to fair or changing task group Message-ID: <20160617021251.GR8105@intel.com> References: <1465942870-28419-1-git-send-email-yuyang.du@intel.com> <1465942870-28419-2-git-send-email-yuyang.du@intel.com> <20160615152217.GN30921@twins.programming.kicks-ass.net> <20160616163013.GA32169@vingu-laptop> <20160616185115.GL30921@twins.programming.kicks-ass.net> <20160616200711.GK30154@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 16, 2016 at 11:21:55PM +0200, Vincent Guittot wrote: > On 16 June 2016 at 22:07, Peter Zijlstra wrote: > > On Thu, Jun 16, 2016 at 09:00:57PM +0200, Vincent Guittot wrote: > >> On 16 June 2016 at 20:51, Peter Zijlstra wrote: > >> > On Thu, Jun 16, 2016 at 06:30:13PM +0200, Vincent Guittot wrote: > >> >> With patch [1] for the init of cfs_rq side, all use cases will be > >> >> covered regarding the issue linked to a last_update_time set to 0 at > >> >> init > >> >> [1] https://lkml.org/lkml/2016/5/30/508 > >> > > >> > Aah, wait, now I get it :-) > >> > > >> > Still, we should put cfs_rq_clock_task(cfs_rq) in it, not 1. And since > >> > we now acquire rq->lock on init this should well be possible. Lemme sort > >> > that. > >> > >> yes with the rq->lock we can use cfs_rq_clock_task which is make more > >> sense than 1. > >> But the delta can be still significant between the creation of the > >> task group and the 1st task that will be attach to the cfs_rq > > > > Ah, I think I've spotted more fail. > > > > And I think you're right, it doesn't matter, in fact, 0 should have been > > fine too! > > > > enqueue_entity() > > enqueue_entity_load_avg() > > update_cfs_rq_load_avg() > > now = clock() > > __update_load_avg(&cfs_rq->avg) > > cfs_rq->avg.last_load_update = now > > // ages 0 load/util for: now - 0 > > if (migrated) > > attach_entity_load_avg() > > se->avg.last_load_update = cfs_rq->avg.last_load_update; // now != 0 > > > > So I don't see how it can end up being attached again. > > In fact it has already been attached during the sched_move_task. The > sequence for the 1st task that is attached to a cfs_rq is : > > sched_move_task() > task_move_group_fair() > detach_task_cfs_rq() > set_task_rq() > attach_task_cfs_rq() > attach_entity_load_avg() > se->avg.last_load_update = cfs_rq->avg.last_load_update == 0 > Then again, does this fix it? static void task_move_group_fair(struct task_struct *p) { detach_task_cfs_rq(p); set_task_rq(p, task_cpu(p)); attach_task_cfs_rq(p); /* * If the cfs_rq's last_update_time is 0, attach the sched avgs * won't be anything useful, as it will be decayed to 0 when any * sched_entity is enqueued to that cfs_rq. * * On the other hand, if the cfs_rq's last_update_time is 0, we * must reset the task's last_update_time to ensure we will attach * the sched avgs when the task is enqueued. */ if (!cfs_rq_of(&p->se)->avg.last_update_time) reset_task_last_update_time(p); else attach_entity_load_avg(cfs_rq_of(&p->se), &p->se); }