Messages in this thread | | | Subject | Re: CFS Bandwidth Control - Test results of cgroups tasks pinned vs unpinnede | From | Peter Zijlstra <> | Date | Tue, 13 Sep 2011 20:23:46 +0200 |
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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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