linux-kernel - Re: [PATCH v3 5/6] Also record sleep start for a task group

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Date:	Wed, 30 May 2012 14:44:37 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Glauber Costa <glommer@...allels.com>
Cc:	Paul Turner <pjt@...gle.com>, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org, devel@...nvz.org,
	Tejun Heo <tj@...nel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>, handai.szj@...il.com,
	Andrew.Phillips@...x.com, Serge Hallyn <serge.hallyn@...onical.com>
Subject: Re: [PATCH v3 5/6] Also record sleep start for a task group

On Wed, 2012-05-30 at 16:24 +0400, Glauber Costa wrote:
> sleep_start is not for iowait. This is for idle. And I know no other way 
> to collect idle time per cgroup, other than the time during which it was 
> out of the runqueue.
> 
> Now what you say about the sleepers don't make that much sense for idle 
> because this information is per-cpu as well.
> 
> When the se is being dequeued, it means none of its children is running 
> on that runqueue. That's idle. 

But does that mean the cgroup is idle? Its impossible to re-construct
the machine state from this per-cpu data if your definition of
cgroup-idle is the time when _all_ cpus are idle.


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