From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754061AbcE3HE0 (ORCPT ); Mon, 30 May 2016 03:04:26 -0400 Received: from mail-lf0-f42.google.com ([209.85.215.42]:36434 "EHLO mail-lf0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753971AbcE3HEY (ORCPT ); Mon, 30 May 2016 03:04:24 -0400 MIME-Version: 1.0 In-Reply-To: <5748B063.4070009@arm.com> References: <1464095335-27730-1-git-send-email-vincent.guittot@linaro.org> <1464188472-30086-1-git-send-email-vincent.guittot@linaro.org> <57486C62.7090205@arm.com> <5748B063.4070009@arm.com> From: Vincent Guittot Date: Mon, 30 May 2016 09:04:02 +0200 Message-ID: Subject: Re: [PATCH v2] sched: fix first task of a task group is attached twice To: Dietmar Eggemann Cc: Peter Zijlstra , Ingo Molnar , linux-kernel , Yuyang Du Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 27 May 2016 at 22:38, Dietmar Eggemann wrote: > On 27/05/16 18:16, Vincent Guittot wrote: >> On 27 May 2016 at 17:48, Dietmar Eggemann wrote: >>> On 25/05/16 16:01, Vincent Guittot wrote: >>>> The cfs_rq->avg.last_update_time is initialize to 0 with the main effect >>>> that the 1st sched_entity that will be attached, will keep its >>>> last_update_time set to 0 and will attached once again during the >>>> enqueue. >>>> Initialize cfs_rq->avg.last_update_time to 1 instead. >>>> >>>> Signed-off-by: Vincent Guittot >>>> --- >>>> >>>> v2: >>>> - rq_clock_task(rq_of(cfs_rq)) can't be used because lock is not held >>>> >>>> kernel/sched/fair.c | 8 ++++++++ >>>> 1 file changed, 8 insertions(+) >>>> >>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >>>> index 218f8e8..3724656 100644 >>>> --- a/kernel/sched/fair.c >>>> +++ b/kernel/sched/fair.c >>>> @@ -8586,6 +8586,14 @@ void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq, >>>> se->depth = parent->depth + 1; >>>> } >>>> >>>> + /* >>>> + * Set last_update_time to something different from 0 to make >>>> + * sure the 1st sched_entity will not be attached twice: once >>>> + * when attaching the task to the group and one more time when >>>> + * enqueueing the task. >>>> + */ >>>> + tg->cfs_rq[cpu]->avg.last_update_time = 1; >>>> + > > Couldn't you not just set the value in init_cfs_rq(): yes, there is no good reason to use init_tg_cfs_entry instead of init_cfs_rq > > @@ -8482,6 +8482,7 @@ void init_cfs_rq(struct cfs_rq *cfs_rq) > cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime; > #endif > #ifdef CONFIG_SMP > + cfs_rq->avg.last_update_time = 1; > atomic_long_set(&cfs_rq->removed_load_avg, 0); > atomic_long_set(&cfs_rq->removed_util_avg, 0); > #endif > >>>> se->my_q = cfs_rq; >>>> /* guarantee group entities always have weight */ >>>> update_load_set(&se->load, NICE_0_LOAD); >>> >>> So why not setting the last_update_time value for those cfs_rq's when >>> we have the lock? E.g. in task_move_group_fair() or attach_task_cfs_rq(). >> >> I'm not sure that it's worth adding this init in functions that are >> then used often only for the init of it. > > Yeah, there will be this if condition overhead. > >> If you are concerned by the update of the load of the 1st task that >> will be attached, it can still have elapsed a long time between the >> creation of the group and the 1st enqueue of a task. This was the case >> for the test i did when i found this issue. > > Understood, but for me, creation of the task group is > cpu_cgroup_css_alloc -> sched_create_group() -> ... -> init_cfs_rq(), > init_tg_cfs_entry(), ... > > and the functions which are called when the first task is put into the > task group are cpu_cgroup_attach() and cpu_cgroup_fork() and they whould > trigger the initial setup of the cfs_rq->avg.last_update_time. > >> >> Beside this point, I have to send a new version to set >> load_last_update_time_copy for not 64 bits system. Fengguang points me >> the issue > > OK. > > [...] >>> >>> + if (!cfs_rq->avg.last_update_time) >>> + cfs_rq->avg.last_update_time = rq_clock_task(rq_of(cfs_rq)); >>> + >>> /* Synchronize task with its cfs_rq */ >>> attach_entity_load_avg(cfs_rq, se); >>