linux-kernel - Re: [PATCH v2] sched: fix first task of a task group is attached twice

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Message-ID: <20160526004046.GJ18670@intel.com>
Date:	Thu, 26 May 2016 08:40:46 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH v2] sched: fix first task of a task group is attached
 twice

On Thu, May 26, 2016 at 10:26:54AM +0200, Vincent Guittot wrote:
> On 26 May 2016 at 00:38, Yuyang Du <yuyang.du@...el.com> wrote:
> > On Wed, May 25, 2016 at 05:01:11PM +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.
> >
> > Actually, the first time (attach_task_cfs_rq()) is called even way
> > before init_entity_runnable_average(), no?
> 
> maybe there is an issue during the fork of a task too
> This patch is about the init of the sched_avg of a task group. The
> problem happens when the 1st task is moved the group but it's not
> about the fork of a task

Right, but the root cause is not addressed, which is when forked, the task
should not be touched on sched avgs before init_entity_runnable_average()
in wake_up_new_task(). You think?