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    SubjectRe: RFC [patch] sched,cgroup_sched: convince RT_GROUP_SCHED throttle to work
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    On Sun, 2012-04-15 at 05:37 +0200, Mike Galbraith wrote: 
    > 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.

    You _could_ bail on !rq->sd I suppose, but the way I hacked around it,
    the user can keep the throttle for testing/troubleshooting their
    isolated setup, and turn it off in production. OTOH, auto throttle
    disable for all isolated sets could work just as well.

    -Mike



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