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

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Date:	Sat, 28 Feb 2009 14:25:22 +0900 (JST)
From:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
To:	"Dhaval Giani" <dhaval@...ux.vnet.ibm.com>
Cc:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
	"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

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.

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


Thanks,
-Kame


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