linux-kernel - Re: [PATCH RFC] [X86] performance improvement for memcpy

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Date:	Tue, 20 Oct 2009 08:33:26 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Ling Ma <linguranus@...il.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] [X86] performance improvement for memcpy_64.S by
	avoid memory miss predication.


* Ling Ma <linguranus@...il.com> wrote:

> Hi Ingo
> Thanks for your suggestion. I used 'perf stat --repeat 10
> /develop/trunk/memcpy/static'  to measure before/after patch.
> 
> The test program I wrote:
>  for (i = 64; i < 4096 *4; i ++)
>       do_memcpy(src, dst, i);
> 
> when src offset is 0xbe000, dst is 0xad008, the measured result:
> 
> Before patch:
>  Performance counter stats for '/develop/trunk/memcpy/static' (10 runs):
>   <not counted>  task-clock-msecs
>   <not counted>  context-switches
>   <not counted>  CPU-migrations
>   <not counted>  page-faults
>   <not counted>  cycles
>   <not counted>  instructions
>   <not counted>  cache-references
>   <not counted>  cache-misses
>    37.408743997  seconds time elapsed   ( +-   0.222% )

hm, on what kind of CPU have you run this? Why are those events not 
counting? Is it some older, Pentium-4 alike CPU perhaps?

	Ingo
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