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

From: Peter Zijlstra
Date: Tue May 31 2016 - 08:04:09 EST

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@xxxxxxxxx> 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
> >
> > 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

Because a quick look seems to suggest something like:

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.. ?