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Date: Sat, 28 Feb 2009 14:25:22 +0900 (JST)
Subject: Re: [PATCH] change cpuacct usage percpu format v2
From: "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@jp.fujitsu.com>
To: "Dhaval Giani" <dhaval@linux.vnet.ibm.com>
Cc: "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@jp.fujitsu.com>,
       "Ken Chen" <kenchen@google.com>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "menage@google.com" <menage@google.com>,
       "lizf@cn.fujitsu.com" <lizf@cn.fujitsu.com>,
       "balbir@linux.vnet.ibm.com" <balbir@linux.vnet.ibm.com>, mingo@elte.hu,
       "akpm@linux-foundation.org" <akpm@linux-foundation.org>
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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