Re: [PATCH] sched/rt: fix SCHED_RR across cgroups

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Wed, 2012-05-16 at 21:34 -0700, Colin Cross wrote:
> task_tick_rt has an optimization to only reschedule SCHED_RR tasks
> if they were the only element on their rq.  However, with cgroups
> a SCHED_RR task could be the only element on its per-cgroup rq but
> still be competing with other SCHED_RR tasks in its parent's
> cgroup.  In this case, the SCHED_RR task in the child cgroup would
> never yield at the end of its timeslice.  If the child cgroup
> rt_runtime_us was the same as the parent cgroup rt_runtime_us,
> the task in the parent cgroup would starve completely.
> 
> Modify task_tick_rt to check that the task is the only task on its
> rq, and that the each of the scheduling entities of its ancestors
> is also the only entity on its rq.
> 
> Signed-off-by: Colin Cross <ccross@android.com>

OK, fair enough.. one does wonder though, WTH is android doing with
SCHED_RR?