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SubjectRe: [PATCH v3] sched: fix first task of a task group is attached twice
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.
> + */
> + cfs_rq->avg.last_update_time = 1;
> +#ifndef CONFIG_64BIT
> + cfs_rq->load_last_update_time_copy = 1;
> +#endif
> atomic_long_set(&cfs_rq->removed_load_avg, 0);
> atomic_long_set(&cfs_rq->removed_util_avg, 0);
> #endif

Then, when enqueued, both cfs_rq and task will be decayed to 0, due to
a large gap between 1 and now, no?

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