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Re: [PATCH v2 2/3] sched/fair: Skip detach and attach new group task

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On Tue, May 31, 2016 at 01:55:49PM +0200, Vincent Guittot wrote:
> Hi Yuyang,
> 
> On 31 May 2016 at 00:32, Yuyang Du <yuyang.du@intel.com> wrote:
> > Vincent reported that the first task to a new task group's cfs_rq will
> > be attached in attach_task_cfs_rq() and once more when it is enqueued
> > (see https://lkml.org/lkml/2016/5/25/388).
> >
> > Actually, it is worse, attach_task_cfs_rq() is invoked for new task even
> > way before the new task is initiated in init_entity_runnable_average().
> >
> > Solve this by avoiding attach as well as detach new task in
> > task_move_group_fair(). To do it, we need to know whether the task
> > is forked or not, so we pass this info all the way from sched_move_task()
> > to attach_task_cfs_rq().
> 
> I have tested your patch and I can't the spurious detach
> /attach_task_cfs_rq anymore
> so you can add my tested-by.
> 

Could someone update the Changelog to better explain the whole
callchain.

Because a quick look seems to suggest something like:

	copy_process()
	  sched_fork()
	  ...
	  cgroup_post_fork()
	    ss->fork() := cpu_cgroup_fork()

Which seems to suggest init_entity_runnable_average() is placed wrong
and should live in sched_fork() ?

Or am I not getting it.. ?

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[PATCH v2 0/3] sched/fair: Skip attach and detach for new group task in task_move_group_fair() Yuyang Du <yuyang.du@intel.com> - 2016-05-31 08:40 +0200
  [PATCH v2 2/3] sched/fair: Skip detach and attach new group task Yuyang Du <yuyang.du@intel.com> - 2016-05-31 08:40 +0200
    Re: [PATCH v2 2/3] sched/fair: Skip detach and attach new group task Vincent Guittot <vincent.guittot@linaro.org> - 2016-05-31 14:00 +0200
      Re: [PATCH v2 2/3] sched/fair: Skip detach and attach new group task Peter Zijlstra <peterz@infradead.org> - 2016-05-31 14:10 +0200
        Re: [PATCH v2 2/3] sched/fair: Skip detach and attach new group task Vincent Guittot <vincent.guittot@linaro.org> - 2016-05-31 14:40 +0200
          Re: [PATCH v2 2/3] sched/fair: Skip detach and attach new group task Peter Zijlstra <peterz@infradead.org> - 2016-05-31 14:50 +0200
            Re: [PATCH v2 2/3] sched/fair: Skip detach and attach new group task Vincent Guittot <vincent.guittot@linaro.org> - 2016-05-31 15:30 +0200
  [PATCH v2 3/3] sched/fair: Add inline to detach_entity_load_evg() Yuyang Du <yuyang.du@intel.com> - 2016-05-31 08:40 +0200

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