linux-kernel - Re: [PATCH] change cpuacct usage percpu format v2

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Message-ID: <20090228092431.GA22310@linux.vnet.ibm.com>
Date:	Sat, 28 Feb 2009 14:54:31 +0530
From:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Ken Chen <kenchen@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"menage@...gle.com" <menage@...gle.com>,
	"lizf@...fujitsu.com" <lizf@...fujitsu.com>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	mingo@...e.hu,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH] change cpuacct usage percpu format v2

On Sat, Feb 28, 2009 at 02:25:22PM +0900, KAMEZAWA Hiroyuki wrote:
> Dhaval Giani wrote：
> > On Sat, Feb 28, 2009 at 09:42:17AM +0900, KAMEZAWA Hiroyuki wrote:
> >> KAMEZAWA Hiroyuki wrote：
> >> BTW, current interface to reset cpuacct (write ops) just reset
> >> specified level of cpuacct and will not clear other hierarchical levels.
> >> Doesn't this behavior confuse software ?
> >>
> >
> > hmmm. This got missed when we introduced hierarchy. But I wonder if it
> > is needed?
> >
> IIUC, cpuacct.usage just shows sum of itself and all children's usage and
> its own usage can be calclated by reading all usage of hierarchy.
> So, reset ops seems to be a bit broken.
> And by this, parent's usage can be smaller than children.
> 

Actually now that I think about it, it does make sense, but when I
started implementing it, a question popped up, if we reset a child's
counter, then the parent is going to have a much greater usage than the
sum of the children. I wonder if this behavior is fine?

> How about adding limitation as "you can clear usage only when there are no
> children" ? Maybe not very strange limitaton under hierarchical system.
> 

Just the question I asked. Beyond that I don't think we should have such a
limitation on reset.

thanks,
-- 
regards,
Dhaval
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