From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933509AbcEaDpX (ORCPT ); Mon, 30 May 2016 23:45:23 -0400 Received: from mga14.intel.com ([192.55.52.115]:56892 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932469AbcEaDpW (ORCPT ); Mon, 30 May 2016 23:45:22 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.26,393,1459839600"; d="scan'208";a="991922567" Date: Tue, 31 May 2016 03:48:02 +0800 From: Yuyang Du To: Vincent Guittot Cc: peterz@infradead.org, mingo@kernel.org, linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com Subject: Re: [PATCH v3] sched: fix first task of a task group is attached twice Message-ID: <20160530194802.GM18670@intel.com> References: <1464623541-25429-1-git-send-email-vincent.guittot@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1464623541-25429-1-git-send-email-vincent.guittot@linaro.org> 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 Mon, May 30, 2016 at 05:52:20PM +0200, 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 > --- > > v3: > - add initialization of load_last_update_time_copy for not 64bits system > - move init into init_cfs_rq > > v2: > - rq_clock_task(rq_of(cfs_rq)) can't be used because lock is not held > > kernel/sched/fair.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 218f8e8..86be9c1 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -8459,6 +8459,16 @@ void init_cfs_rq(struct cfs_rq *cfs_rq) > cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime; > #endif > #ifdef CONFIG_SMP > + /* > + * 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. > + */ The first time: "once when attaching the task to the group". That attaching is purely wrong, but will not have any effect (at least load/util wise), because the task will later be inited in init_entity_runnable_average(). The second time: "one more time when enqueueing the task". In enqueue_entity_load_avg(), your patch will not have any effect either, because of the above overwriting the new task's load in init_entity_runnable_average(), no?