linux-kernel - Re: [PATCH 6/9] Include idle and iowait fields in cpuacct

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Message-ID: <4E7888B8.3080809@parallels.com>
Date:	Tue, 20 Sep 2011 09:36:08 -0300
From:	Glauber Costa <glommer@...allels.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	<linux-kernel@...r.kernel.org>, <xemul@...allels.com>,
	<paul@...lmenage.org>, <lizf@...fujitsu.com>,
	<daniel.lezcano@...e.fr>, <mingo@...e.hu>,
	<jbottomley@...allels.com>
Subject: Re: [PATCH 6/9] Include idle and iowait fields in cpuacct

On 09/20/2011 06:21 AM, Peter Zijlstra wrote:
> On Wed, 2011-09-14 at 17:04 -0300, Glauber Costa wrote:
>> These are slightly different from the others though:
>> (note to reviewers: might be better to put those in a separate
>> array?)
>>
>> Since idle/iowait are a property of the system - by definition,
>> no process from any cgroup is running when the system is idle,
>> they are system wide. So what these fields really mean, are baselines
>> for when the cgroup was created. It allows the cgroup to start
>> counting idle/iowait from 0.
>
> Alternatively you can make iowait based on nr_uninterruptible per cgroup
> and count all ticks _this_ cgroup was idle.
You think?

Humm,humm... maybe...
iowait can indeed be seen as a process group characteristic. I was 
mainly concerned about overhead here, specially for the idle case:

If we are idle, there is no task context we can draw from, since the 
task in the cpu is the idle task. So we end up having to touch all 
cgroups... Or am I missing something?

Sounds expensive.


> Now all that would need moar accounting...

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