linux-kernel - Re: [PATCH] cpuidle: menu: use nr_running instead of cpuload for calculating perf mult

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Message-ID: <9511B40F-7F71-4A99-87B8-4CD88C83FE4E@parallels.com>
Date:	Mon, 4 Jun 2012 17:19:08 +0400
From:	Vladimir Davydov <VDavydov@...allels.com>
To:	Arjan van de Ven <arjan@...ux.intel.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Len Brown <lenb@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpuidle: menu: use nr_running instead of cpuload for
 calculating perf mult

On Jun 4, 2012, at 5:15 PM, "Arjan van de Ven" <arjan@...ux.intel.com> wrote:

> On 6/4/2012 3:24 AM, Vladimir Davydov wrote:
>> rq->cpuload strongly depends on cgroup hierarchy. For example, if hundreds of
>> tasks are running inside cpu:/test cgroup, the sum of cpuload over all cpus
>> won't exceed 1024 (by default). That makes the cpuidle menu governor take wrong
>> decisions, which can negatively affect overall performance.
> 
> nr_running is the wrong answer... it is instantaneous, not longer term.
> cpuidle wants a longer term, per cpu, notion of "busy", to use as proxy
> for performance sensitivity.
> 
> 

I use not the instantaneous nr_running, but nr_running last seen in update_cpu_load() where cpuload[0], which is currently used by cpuidle, is updated.

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