linux-kernel - Re: [PATCH V2 -tip] lib,x86_64: improve the performance of memcpy() for unaligned copy

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Date:	Mon, 18 Oct 2010 14:23:55 +0800
From:	Miao Xie <miaox@...fujitsu.com>
To:	"Ma, Ling" <ling.ma@...el.com>
CC:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Zhao, Yakui" <yakui.zhao@...el.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 -tip] lib,x86_64: improve the performance of memcpy()
 for unaligned copy

On Fri, 15 Oct 2010 03:43:53 +0800, Ma, Ling wrote:
> Attachment includes memcpy-kernel.c(cc -O2 memcpy-kernel.c -o memcpy-kernel),
> and unaligned test cases on Atom.

I have tested on my Core2 Duo machine with your benchmark tool. Attachment is the
test result. But the result is different with yours on Atom, It seems the performance
is better with this patch.

According to these two different result, maybe we need optimize memcpy() by CPU
model.

Thanks
Miao

>
> Thanks
> Ling
>
> -----Original Message-----
> From: Ma, Ling
> Sent: Thursday, October 14, 2010 9:14 AM
> To: 'H. Peter Anvin'; miaox@...fujitsu.com
> Cc: Ingo Molnar; Andi Kleen; Thomas Gleixner; Zhao, Yakui; Linux Kernel
> Subject: RE: [PATCH V2 -tip] lib,x86_64: improve the performance of memcpy() for unaligned copy
>
> Sure, I will post benchmark tool and benchmark on Atom 64bit soon.
>
> Thanks
> Ling
>
> -----Original Message-----
> From: H. Peter Anvin [mailto:hpa@...or.com]
> Sent: Thursday, October 14, 2010 5:32 AM
> To: miaox@...fujitsu.com
> Cc: Ma, Ling; Ingo Molnar; Andi Kleen; Thomas Gleixner; Zhao, Yakui; Linux Kernel
> Subject: Re: [PATCH V2 -tip] lib,x86_64: improve the performance of memcpy() for unaligned copy
>
> On 10/08/2010 02:02 AM, Miao Xie wrote:
>> On Fri, 8 Oct 2010 15:42:45 +0800, Ma, Ling wrote:
>>> Could you please give us full address for each comparison result,we will do some tests on my machine.
>>> For unaligned cases older cpus will crossing cache line and slow down caused by load and store, but for nhm, no necessary to care about it.
>>> By the way in kernel 64bit mode, our access mode should be around 8byte aligned.
>>
>> Would you need my benchmark tool? I think it is helpful for your test.
>>
>
> If you could post the benchmark tool that would be great.
>
> 	-hpa


View attachment "memcpy-Core2-Duo-CPU-unaligned-result" of type "text/plain" (11009 bytes)