linux-kernel - Re: RFC [patch] sched,cgroup_sched: convince RT_GROUP

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Date:	Sun, 15 Apr 2012 05:37:41 +0200
From:	Mike Galbraith <efault@....de>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>
Subject: Re: RFC [patch] sched,cgroup_sched: convince RT_GROUP_SCHED
 throttle to work

On Sat, 2012-04-14 at 13:10 +0200, Peter Zijlstra wrote: 
> On Tue, 2012-04-10 at 11:08 +0200, Mike Galbraith wrote:
>  
> > --- a/kernel/sched/rt.c
> > +++ b/kernel/sched/rt.c
> > @@ -782,6 +782,19 @@ static int do_sched_rt_period_timer(stru
> >  	const struct cpumask *span;
> >  
> >  	span = sched_rt_period_mask();
> > +#ifdef CONFIG_RT_GROUP_SCHED
> > +	/*
> > +	 * FIXME: isolated CPUs should really leave the root task group,
> 
> No no, that's the wrong fix, the right fix is to remove isolcpus :-)

Yeah, isolcpus needs to die, but...

> I guess the alternative 'fix' is to not account the rt_runtime on
> isolated cpus.. does something like the below actually work?

I haven't tried it, because the exact same thing happens when you
isolate via cpusets directly below root.  One timer, two (or more)
rd->span, so _somebody_ is screwed.

-Mike

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