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

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Message-ID: <20081030171622.GA19872@linux.vnet.ibm.com>
Date:	Thu, 30 Oct 2008 22:46:22 +0530
From:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	bharata@...ux.vnet.ibm.com,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.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 Mon, Oct 27, 2008 at 04:25:01PM +0800, Li Zefan wrote:
> >>>> So in technical terms this patch looks fine now. There's still the
> >>>> question of whether it's OK to change the existing API, since it's
> >>>> been in the kernel in its currently (non-hierarchical) form for
> >>>> several releases now.
> >> Hmm... Can we consider this as an API change ? Currently cpuacct.usage
> >> readers of a parent accounting group are missing the usage contributions
> >> from its children groups. I would consider this patch as fixing the
> >> above problem by correctly reflecting the cpu usage for every accounting
> >> group.
> >>
> > 
> > If a particular application desires to derive the usage of its
> > immediate tasks and does not care about subcgroups, it is a simple
> > iteration (after this fix)
> > 
> > cpuacct - sigma(cpuacct_child)
> > 
> > and currently if we cared about child accounting, we could do
> > 
> > cpuacct + recursively(sigma(cpuacct_child))
> > 
> > In that sense this fix makes more sense, but like Paul said we need to
> > figure out if it is an API change. My take is that it is a BUG fix,
> > since we do care about child subgroups in accounting.
> > 
> 
> 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.

Thanks,
-- 
regards,
Dhaval
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