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    SubjectRe: CFS Bandwidth Control - Test results of cgroups tasks pinned vs unpinnede
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    On Tue, 2011-09-13 at 23:31 +0530, Srivatsa Vaddagiri wrote:
    > * Peter Zijlstra <a.p.zijlstra@chello.nl> [2011-09-13 16:19:39]:
    >
    > > > Booting with "nohz=off" also helps significantly.
    > > >
    > > > With nohz=on, average idle time (over 1 min) is 10.3%
    > > > With nohz=off, average idle time (over 1 min) is 3.9%
    > >
    > > So we should put the cpufreq/idle governor into the nohz/idle path, it
    > > already tries to predict the idle duration in order to pick a C state,
    > > that same prediction should be used to determine if stopping the tick is
    > > worth it.
    >
    > Hmm ..I tried performance governor and found that it slightly increases
    > idle time.
    >
    > With nohz=off && ondemand governor, idle time = 4%
    > With nohz=off && performance governor on all cpus, idle time = 6%
    >
    > I can't see obvious reasons for that ..afaict bandwidth capping should
    > be independent of frequency (i.e task gets capped by "used" time,
    > irrespective of frequency at which it was "using" the cpu)?

    That's not what I said.. what I said is that the nohz code should also
    use the idle time prognosis.. disabling the tick is a costly operation,
    doing it only to have to undo it costs time, and will be accounted to
    idle time, hence your improvement with nohz=off.




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