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

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Message-ID: <5125AEE6.5030706@linux.vnet.ibm.com>
Date:	Thu, 21 Feb 2013 13:21:42 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Mike Galbraith <efault@....de>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	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 02/20/2013 10:05 PM, Mike Galbraith wrote:
> On Wed, 2013-02-20 at 14:32 +0100, 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 ;-)
> 
> (yeah, I mentioned that needs to shrink.. a lot)

Exactly, and I'm going to apply the suggestion now :)

> 
>>> 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.
> 
> Yup, even little stuff like break off the search when load is zero..

Agree, searching in a bunch of idle cpus and their subsets doesn't make
sense...

Regards,
Michael Wang

> unless someone is planning on implementing anti-idle 'course ;-)
> 
> -Mike
> 
> 
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