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

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Date:	Sat, 19 May 2012 15:11:02 +0200
From:	Dario Faggioli <raistlin@...ux.it>
To:	Colin Cross <ccross@...roid.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	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, 2012-05-18 at 17:13 -0700, Colin Cross wrote: 
> 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.
> 
That looks right to me...

> Is that the way SCHED_RR is intended to interact with cgroups?
>
I would say it is. That's what you get because of putting task1 and
cgroup at the same level in the "hierarchy". I'm curious, what kind of
behaviour were you expecting?

Of course, the actual schedule also depends on the real-time priority of
the various tasks (groups don't have a priority, they inherit it from
their tasks, or at least it was like this when I used to work with
it :-P), but I guess you're putting all the tasks in the same queue
(i.e., same rt-prio), is it that the case?

Dario

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-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://retis.sssup.it/people/faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://retis.sssup.it/people/faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)



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