linux-kernel - Re: [PATCH] sched/rt: fix SCHED

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Date:	Fri, 18 May 2012 17:13:28 -0700
From:	Colin Cross <ccross@...roid.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Hillf Danton <dhillf@...il.com>
Subject: Re: [PATCH] sched/rt: fix SCHED_RR across cgroups

On Fri, May 18, 2012 at 11:37 AM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> On Fri, 2012-05-18 at 10:52 -0700, Colin Cross wrote:
>
>> > OK, fair enough.. one does wonder though, WTH is android doing with
>> > SCHED_RR?
>>
>> Nothing, I was just experimenting with how it interacted with cgroups
>> and the numbers didn't make sense.
>
> OK. Thanks anyway!

Even with this patch, scheduling of SCHED_RR tasks in cgroups is a
little odd.  Each cgroup is treated as a schedulable entity alongside
the tasks in the same parent cgroup, and then the tasks inside the
child cgroup round robin through the child cgroup's time slices.  So
in the setup:
root_cgroup
   task 1
   cgroup
      task 2
      task 3

The RR will be:
task 1, cgroup(task 2), task 1, cgroup(task 3), ...

task 1 will run twice as often, for a full RR_TIMESLICE each time, as
tasks 2 and 3.

Is that the way SCHED_RR is intended to interact with cgroups?
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