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Re: [PATCH v3] sched: fix first task of a task group is attached twice

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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 <vincent.guittot@linaro.org>
> ---
> 
> 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?

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[PATCH] sched: fix first task of a task group is attached twice Vincent Guittot <vincent.guittot@linaro.org> - 2016-05-24 15:10 +0200
  [PATCH v2] sched: fix first task of a task group is attached twice Vincent Guittot <vincent.guittot@linaro.org> - 2016-05-25 17:10 +0200
    Re: [PATCH v2] sched: fix first task of a task group is attached  twice Yuyang Du <yuyang.du@intel.com> - 2016-05-26 08:40 +0200
      Re: [PATCH v2] sched: fix first task of a task group is attached twice Vincent Guittot <vincent.guittot@linaro.org> - 2016-05-26 10:30 +0200
        Re: [PATCH v2] sched: fix first task of a task group is attached  twice Yuyang Du <yuyang.du@intel.com> - 2016-05-26 10:40 +0200
          Re: [PATCH v2] sched: fix first task of a task group is attached twice Vincent Guittot <vincent.guittot@linaro.org> - 2016-05-26 11:00 +0200
    Re: [PATCH v2] sched: fix first task of a task group is attached  twice Dietmar Eggemann <dietmar.eggemann@arm.com> - 2016-05-27 17:50 +0200
      Re: [PATCH v2] sched: fix first task of a task group is attached twice Vincent Guittot <vincent.guittot@linaro.org> - 2016-05-27 19:20 +0200
        Re: [PATCH v2] sched: fix first task of a task group is attached  twice Dietmar Eggemann <dietmar.eggemann@arm.com> - 2016-05-27 22:40 +0200
          Re: [PATCH v2] sched: fix first task of a task group is attached twice Vincent Guittot <vincent.guittot@linaro.org> - 2016-05-30 09:10 +0200
            [PATCH v3] sched: fix first task of a task group is attached twice Vincent Guittot <vincent.guittot@linaro.org> - 2016-05-30 18:00 +0200
              Re: [PATCH v3] sched: fix first task of a task group is attached  twice Yuyang Du <yuyang.du@intel.com> - 2016-05-31 05:50 +0200
                Re: [PATCH v3] sched: fix first task of a task group is attached twice Vincent Guittot <vincent.guittot@linaro.org> - 2016-05-31 09:30 +0200
                Re: [PATCH v3] sched: fix first task of a task group is attached  twice Yuyang Du <yuyang.du@intel.com> - 2016-05-31 10:50 +0200
              Re: [PATCH v3] sched: fix first task of a task group is attached  twice Dietmar Eggemann <dietmar.eggemann@arm.com> - 2016-06-01 17:40 +0200
                Re: [PATCH v3] sched: fix first task of a task group is attached twice Vincent Guittot <vincent.guittot@linaro.org> - 2016-06-01 18:00 +0200
                Re: [PATCH v3] sched: fix first task of a task group is attached  twice Dietmar Eggemann <dietmar.eggemann@arm.com> - 2016-06-06 21:40 +0200
                Re: [PATCH v3] sched: fix first task of a task group is attached twice Vincent Guittot <vincent.guittot@linaro.org> - 2016-06-07 09:40 +0200
          Re: [PATCH v2] sched: fix first task of a task group is attached twice Vincent Guittot <vincent.guittot@linaro.org> - 2016-05-30 18:00 +0200

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