linux-kernel - Re: [PATCH 1/9] Remove parent field in cpuacct cgroup

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Message-ID: <4E778C0E.5060000@parallels.com>
Date:	Mon, 19 Sep 2011 15:38:06 -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 1/9] Remove parent field in cpuacct cgroup

On 09/19/2011 03:35 PM, Peter Zijlstra wrote:
> On Mon, 2011-09-19 at 13:30 -0300, Glauber Costa wrote:
>> For cpuusage, I am not sure this optimization is a valid one
>
> I was talking about cpuusage, cpuacct_charge() is called for every
> ctxsw/tick.

I am not touching it right now.

> But even for cpuacct tick stuff, wouldn't you need to sum all your child
> cgroups to update the current cgroup? and that up the whole tree?

Of course I would. But as I said, it does not need to be done every 
tick, in case it poses such a cacheline mayhem as you fear.

Since we'll only really need those values when someone reads it - which 
is a far less frequent operation than the tick resolution - and when a 
cgroup is destroyed - even less frequent operation - it should work well.
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