linux-kernel - Re: Big git diff speedup by avoiding x86 "fast string" memcmp

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Message-ID: <20101215043840.GA7692@cr0.nay.redhat.com>
Date:	Wed, 15 Dec 2010 12:38:40 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Nick Piggin <npiggin@...il.com>
Cc:	"J. R. Okajima" <hooanon05@...oo.co.jp>,
	Nick Piggin <npiggin@...nel.dk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: Big git diff speedup by avoiding x86 "fast string" memcmp

On Mon, Dec 13, 2010 at 07:25:05PM +1100, Nick Piggin wrote:
>On Mon, Dec 13, 2010 at 6:29 PM, J. R. Okajima <hooanon05@...oo.co.jp> wrote:
>> But is the "rep cmp has quite a long latency" issue generic for all x86
>> architecture, or Westmere system specific?
>
>I don't believe it is Westmere specific. Intel and AMD have
>been improving these instructions in the past few years, so
>Westmere is probably as good or better than any.
>
>That said, rep cmp may not be as heavily optimized as the
>set and copy string instructions.
>
>In short, I think the change should be suitable for all x86 CPUs,
>but I would like to hear more opinions or see numbers for other
>cores.
>

How about other arch? If this is only for x86, shouldn't it be
protected by CONFIG_X86?

Thanks.
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