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Message-ID: <C10D3FB0CD45994C8A51FEC1227CE22F15D77722D0@shsmsx502.ccr.corp.intel.com>
Date: Mon, 18 Oct 2010 16:01:13 +0800
From: "Ma, Ling" <ling.ma@...el.com>
To: "miaox@...fujitsu.com" <miaox@...fujitsu.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
>> rep_good will cause memcpy jump to memcpy_c, so not run this patch,
>> we may continue to do further optimization on it later.
>Yes, but in fact, the performance of memcpy_c is not better on some micro-architecture(such as:
>Wolfdale-3M, ), especially in the unaligned cases, so we need do optimization for it, and I think
>the first step of optimization is optimizing the original code of memcpy().
As mentioned above , we will optimize further memcpy_c soon.
Two reasons :
1. movs instruction need long lantency to startup
2. movs instruction is not good for unaligned case.
>> BTW the improvement is only from core2 shift register optimization,
>> but for most previous cpus shift register is very sensitive because of decode stage.
>> I have test Atom, Opteron, and Nocona, new patch is still better.
>I think we can add a flag to make this improvement only valid for Core2 or other CPU like it,
>just like X86_FEATURE_REP_GOOD.
We should optimize core2 in memcpy_c function in future, I think.
Thanks
Ling
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