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

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Date:	Thu, 21 Feb 2013 13:14:37 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>, Mike Galbraith <efault@....de>,
	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 02/20/2013 09:32 PM, Peter Zijlstra wrote:
> On Wed, 2013-02-20 at 11:49 +0100, Ingo Molnar wrote:
> 
>> The changes look clean and reasoable, 
> 
> I don't necessarily agree, note that O(n^2) storage requirement that
> Michael failed to highlight ;-)

Forgive me for not explain this point in cover, but it's really not a
big deal in my opinion...

And I'm going to apply Mike's suggestion, do allocation when cpu active,
that will save some space :)

Regards,
Michael Wang

> 
>> any ideas exactly *why* it speeds up?
> 
> That is indeed the most interesting part.. There's two parts to
> select_task_rq_fair(), the 'regular' affine wakeup path, and the
> fork/exec find_idlest_goo() path. At the very least we need to quantify
> which of these two parts contributes most to the speedup.
> 
> In the power balancing discussion we already noted that the
> find_idlest_goo() is in need of attention.
> 
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