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

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Message-ID: <0c61acc4a0951c46262d52a8eec4db32.squirrel@webmail-b.css.fujitsu.com>
Date:	Sat, 28 Feb 2009 18:37:08 +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 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?
>
As far as the user remembers he did reset...

>> 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.
>
Ok, I don't have strong requirements. I'll recomend users that you should
reset all children(hierarchy) at the same time.

Maybe no problem if we have private-usage counter....but it means one more
percpu array...

Thanks,
-Kame



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