linux-kernel - Re: [PATCH V2 1/3] lib: introduce some memory copy macros and functions

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Date:	Wed, 08 Sep 2010 21:32:42 +0800
From:	Miao Xie <miaox@...fujitsu.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Theodore Ts'o" <tytso@....edu>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Ext4 <linux-ext4@...r.kernel.org>,
	Linux Btrfs <linux-btrfs@...r.kernel.org>
Subject: Re: [PATCH V2 1/3] lib: introduce some memory copy macros and   
   functions

On Wed, 8 Sep 2010 15:05:19 +0200, Andi Kleen wrote:
> On Wed, 08 Sep 2010 20:57:07 +0800
> Miao Xie<miaox@...fujitsu.com>  wrote:
>
>> On Wed, 8 Sep 2010 14:19:25 +0200 (cest), Andi Kleen wrote:
>>>
>>>> According to the data, the length of the most copies is>=128.
>>>
>>> Thanks for the data. Large is easier to optimize than small, that's
>>> good.
>>>
>>> Could you also measure how many memsets need the backwards copy?
                                     ^^^^^^^ :-)
>>> (should be easy to add)
>>
>> I think memset doesn't need the backwards copy.
>
> I meant for memmove of course. Obviously memset doesn't need a backwards
> copy. That was just the only thing the script didn't measure because
> the original version didn't have memmove support.

memmove
total 5224252
[snip]

forward copy
value |-------------------------------------------------- count
     0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@  980253


backward copy
value |-------------------------------------------------- count
     0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@  4243999

the backward copy is much more than the forward copy.

Thanks
Miao


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