Re: [PATCH v5 4/5] sched/fair: Skip detach sched avgs for new task when changing task groups

[Peter Zijlstra]

On Thu, Jun 09, 2016 at 07:15:53AM +0800, Yuyang Du wrote:
> Newly forked task has not been enqueued, so should not be removed from
> cfs_rq in task_move_group_fair(). To do so, we identify newly forked
> tasks by their sched_avg's last_update_time in detach_entity_load_avg().

>  static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct 
> sched_entity *se)
>  {
> +     /* Newly forked tasks are not attached yet. */
> +     if (!se->avg.last_update_time)
> +             return;

Urgh, so this results in two different heuristics to detect 'new' tasks
and gives two different meanings to !last_update_time.

How about you use the existing heuristic as per vruntime_normalized()
and do:

        if (!se->sum_exec_runtime)
                return;