linux-kernel - Re: [RFC PATCH v3 0/3] sched: simplify the select_task_rq

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Date:	Fri, 22 Feb 2013 17:58:27 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Mike Galbraith <efault@....de>, Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>, alex.shi@...el.com,
	Ram Pai <linuxram@...ibm.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [RFC PATCH v3 0/3] sched: simplify the select_task_rq_fair()

On 02/22/2013 05:39 PM, Peter Zijlstra wrote:
> On Fri, 2013-02-22 at 17:10 +0800, Michael Wang wrote:
>> On 02/22/2013 04:21 PM, Peter Zijlstra wrote:
>>> On Fri, 2013-02-22 at 10:36 +0800, Michael Wang wrote:
>>>> According to my understanding, in the old world, wake_affine() will
>>>> only
>>>> be used if curr_cpu and prev_cpu share cache, which means they are in
>>>> one package, whatever search in llc sd of curr_cpu or prev_cpu, we
>>>> won't
>>>> have the chance to spread the task out of that package.
>>>
>>> Nah, look at where SD_WAKE_AFFINE is set. Only 'remote/big' NUMA domains
>>> don't have it set, but 'small' NUMA systems will have it set over the
>>> entire domain tree.
>>
>> Oh, I missed that point...
>>
>> But I don't get the reason to make NUMA level affine, cpus in different
>> nodes share cache? doesn't make sense...
> 
> Contrary, it makes more sense, the more expensive it is to run 'remote'
> the better it is to pull 'related' tasks together.

It increase the range to bound task, from one node to several, but also
increase the range of target cpus, from one node's to several's, I still
can't estimate the benefit, but I think I get the purpose, trying to
make related tasks as close as possible, is that right?

Let me think about this point, I do believe there will be better way to
take care of this purpose.

Regards,
Michael Wang


> 
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