linux-kernel - Re: CFS Bandwidth Control - Test results of cgroups tasks pinned vs unpinnede

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Date:	Tue, 13 Sep 2011 23:31:46 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Paul Turner <pjt@...gle.com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	Dhaval Giani <dhaval.giani@...il.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Pavel Emelianov <xemul@...allels.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: CFS Bandwidth Control - Test results of cgroups tasks pinned vs
 unpinnede

* Peter Zijlstra <a.p.zijlstra@...llo.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)?

- vatsa
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