linux-kernel - Re: [PATCH] remove rq->lock from cpuacct cgroup v2

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Date:	Wed, 4 Mar 2009 16:05:14 +0530
From:	Bharata B Rao <bharata.rao@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	paulmck@...ux.vnet.ibm.com, Li Zefan <lizf@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>, Paul Menage <menage@...gle.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>, kenchen@...gle.com
Subject: Re: [PATCH] remove rq->lock from cpuacct cgroup v2

On Wed, Mar 4, 2009 at 2:16 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> On Wed, 4 Mar 2009 17:20:05 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
>
>> On Wed, 4 Mar 2009 13:24:43 +0530
>> Bharata B Rao <bharata.rao@...il.com> wrote:
>> At first, generic per-cpu counter sounds interesting but to be honest,
>> some special handling is used for cpuacct based on its characteristic.
>>
>>   - Writer works under non-preemptable context.
>>   - There is only one writer.
>>
> If utime/stime updates works on above context, using the same code will be good.

IIUC, utime/stime updates also work under the above conditions.

>
> I don't use any cpuacct structure specific in routines...
> If you want me to rewrite it, I'll do. please request what you want.

After looking deep into your patch, I think I could use the same seq
counter introduced by you to update stime/utime also.
I guess I could use most part of your code except there is a slight
difference wrt preemption disabled assumption in the write path.
cpusuage updates happen under rq->lock but stime/utime updates don't.
So I probably can't use cpuacct_start/end_counter_update as is.

Regards,
Bharata.
-- 
http://bharata.sulekha.com/blog/posts.htm
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