Messages in this thread | | | Date | Fri, 16 Sep 2011 01:14:32 -0700 | From | Paul Turner <> | Subject | Re: CFS Bandwidth Control - Test results of cgroups tasks pinned vs unpinnede |
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On 09/13/11 11:23, Peter Zijlstra wrote: > 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%
I think more compelling here is that it looks like nohz load-balance needs more love.
>>> >>> 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. >
Enabling Venki's CONFIG_IRQ_TIME_ACCOUNTING=y would discount to provide a definitive answer here yes?
- Paul
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