Re: [PATCH] cpuacct: add a branch prediction

From: Bharata B Rao <bharata.rao@gmail.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>, Ingo Molnar <mingo@elte.hu>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Paul Menage <menage@google.com>,
	Balbir Singh <balbir@linux.vnet.ibm.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] cpuacct: add a branch prediction
Date: Thu, 26 Feb 2009 15:40:23 +0530	[thread overview]
Message-ID: <344eb09a0902260210y44c0684by9b22f041116d3f7c@mail.gmail.com> (raw)
In-Reply-To: <20090226174033.094e4834.kamezawa.hiroyu@jp.fujitsu.com>

On Thu, Feb 26, 2009 at 2:10 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Thu, 26 Feb 2009 16:35:33 +0800
> Li Zefan <lizf@cn.fujitsu.com> wrote:
>
>> ca is not checked before hierarchy support, and it's a side-effect.
>>
>> Before cpuacct is initialized, css == task->cgroups->subsys[cpuacct_subsys] == NULL,
>> but ca = task_ca(tsk) is not necessarily NULL, unless struct cgroup_subsys_state is the
>> first member of struct cpuacct.
>>
>> And the above code actually should be:
>>
>> do {
>>       ...
>> } while (ca->parent);
>>
> I'll send no more objections to this patch itself.
>
> But IMHO, this loop is tooo bad, I think. The hierarchy information should be gathered by
> read-side and the total code should be

How do you take care of accounting when a group gets deleted ?.
Wouldn't you loose some information due to deleted groups if you want
to accumulate hierarchical stats only during read ?

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