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

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Message-ID: <4F260BFE.2070503@linux.vnet.ibm.com>
Date:	Mon, 30 Jan 2012 11:18:22 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Cong Wang <xiyou.wangcong@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Xiaotian Feng <xtfeng@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] sched: Accelerate "pick_next_entity" under special
 condition

On 01/30/2012 12:33 AM, Ingo Molnar wrote:

> 
> * Michael Wang <wangyun@...ux.vnet.ibm.com> wrote:
> 
>> On 01/27/2012 12:42 PM, Cong Wang wrote:
>>
>>> On 01/27/2012 09:22 AM, Michael Wang wrote:
>>>> Hi, Ingo
>>>>
>>>> Thanks for your reply.
>>>>
>>>> I have try use "ls -l" to see the size of sched.o, but after applied the
>>>> patch, it is still 1636.
>>>>
>>>> I have not use this method before, may be I use the wrong command...
>>>>
>>>> But I think the new code should be similar to the old one after compile,
>>>> because we still have 3 condition check here.
>>>>
>>>> I suppose the new sched.o will be a little bigger, because one jump
>>>> command and a label need to be added.
>>>>
>>>
>>> Try to see if `size` helps.
>>
>> Hi, Cong
>>
>> Thanks for your advise, but still, the size not changed.
>>
>> And also I don't know whether the size can be some kind of 
>> proof to confirm the performance improvement in this case...
> 
> You could disassemble the .o file via objdump -d and run diff on 
> it - is there any change in the code generated by GCC?
> 
> Thanks,
> 
> 	Ingo
> 

This tool is great :)
But the sched.o under ./arch/x86/kernel/cpu/ still not change...
I think I may checking the wrong file, because this patch is for fair.c.

And the fair.o changed after apply the patch, the size is a little
bigger, and the gcc generated code changed.

But I still don't know what can we get from this result? Bigger size is
caused by additional code, but these additional code will help to step
over some unnecessary code under special condition, looks like some
balance between size and performance...

Regards,
Michael Wang

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