linux-kernel - Re: [PATCH v2] sched: Accelerate "pick_next

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Message-ID: <4F21F638.2080306@linux.vnet.ibm.com>
Date:	Fri, 27 Jan 2012 08:56:24 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Xiaotian Feng <xtfeng@...il.com>, ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] sched: Accelerate "pick_next_entity" under special
 condition

On 01/25/2012 11:55 PM, Peter Zijlstra wrote:

> On Tue, 2012-01-17 at 11:04 +0800, Michael Wang wrote:
>>
>>> Then what if condition 1 is true now?
>>
>> We can see in original code, even condition 1 is true, we
>> still will use value3 if condition3 is true, like this:
>>
>> original:
>>
>> condition1      condition3      result
>> true            true            value3
>> true            false           value1
>>
>> That means if condition3 is true, we don't care whether
>> condition1 is true or not because we will finally use value3.
> 

> Right, so from the original 8 possible states we used to evaluate 3*8 =
> 24 conditionals. The new code will reduce this to 1*4 + 2*2 + 2*3 = 14.
> 
> Now I guess the question is if it matters for the modal or average
> state.
> 


Hi, Peter

I think how much help this patch can do on the performance depends on
how often the condition2 and 3 occur.

> I've applied the patch since it can't be worse, but I've no idea if it
> matters or not in practice.


It's hardly to say how useful this patch is, but it will do some help
under special condition.
Thanks for your review.

Regards,
Michael Wang

> 


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