linux-kernel - Re: [PATCH] Add hierarchical accounting to cpu accounting controller

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Date:	Wed, 5 Nov 2008 12:48:54 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	bharata@...ux.vnet.ibm.com, Paul Menage <menage@...gle.com>,
	linux-kernel@...r.kernel.org,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] Add hierarchical accounting to cpu accounting
 controller

On Wed, 05 Nov 2008 11:31:32 +0800
Li Zefan <lizf@...fujitsu.com> wrote:

> >> cpuacct was designed to count cpu usage of a group of tasks, and now some people
> >> want it to also take child group's usage into account, so I think this is a feature
> >> request but not a bug fix.
> >>
> > 
> > I disagree. The child is a part of the parent's hierarchy, and therefore
> > its usage should reflect in the parent's usage.
> > 
> 
> In memcg the child's usage doesn't reflect in its parent's usage. ;)
> 
> Balbir just posted a patchset to add hierarchy support in memcg, and added memory.feature
> to disable/enable this feature. Is it for performance only or also for keeping the user
> interface/behavior unchanged?

The main reason is performance.

And one of memcg's purpose is isolating resource usage of groups. Sum of usage
is not very important sometimes. (we have /proc/meminfo ;)
Sum of usage can be easily calculcated by user land and we don't have to pay
the cost for it in the kernel.

Thanks,
-Kame

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