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Subject: Re: CFS Bandwidth Control - Test results of cgroups tasks pinned vs
 unpinnede
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Paul Turner <pjt@google.com>
Cc: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
        Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>,
        Vladimir Davydov <vdavydov@parallels.com>,
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        Bharata B Rao <bharata@linux.vnet.ibm.com>,
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        Ingo Molnar <mingo@elte.hu>, Pavel Emelianov <xemul@parallels.com>,
        Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 16 Sep 2011 10:28:40 +0200
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On Fri, 2011-09-16 at 01:14 -0700, Paul Turner wrote:
> 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.

Quite probable, although I do know we tend to go overboard in going into
nohz state too.

> > 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?

Ah, yes, its all (soft)irq context anyway, no need to also account
systemcalls.