linux-kernel - Re: [PATCH v2 14/14] Change CPUACCT to default n

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Date:	Fri, 25 Nov 2011 11:19:20 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Balbir Singh <bsingharora@...il.com>
Cc:	Glauber Costa <glommer@...allels.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Paul Turner <pjt@...gle.com>, linux-kernel@...r.kernel.org,
	paul@...lmenage.org, lizf@...fujitsu.com, daniel.lezcano@...e.fr,
	jbottomley@...allels.com, fweisbec@...il.com
Subject: Re: [PATCH v2 14/14] Change CPUACCT to default n

On Fri, 2011-11-25 at 11:08 +0530, Balbir Singh wrote:
> It is not about $customer. I am OK with a design that allows
> accounting independent of control. Put it another way when I look at
> cgroups, I see the following functionality
> 
> 1. Accounting and feedback
> 2. Control
> 
> Why do 1 and 2 have to co-exist. A good case would be that we might
> need just stats and might want to implement control based on 1.

I would say that 2 always requires 1 (provided they are of course on the
same subject), for the very simple reason that you need to know the
current state (as provided by 1) to control it (2).

Therefore separating them leads to useless duplication.

> But if
> I have to do both 1 and 2 together, how do we decide on control
> values? 

Uh, what?

What was not answered is, is there a sane reason to have both on
different hierarchies? I think the whole different hierarchy per
controller thing is one of the biggest trainwrecks of cgroups.

It allows for great confusion, but I haven't yet seen an up-side to it.
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