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

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Message-ID: <9580.1292225351@jrobl>
Date:	Mon, 13 Dec 2010 16:29:11 +0900
From:	"J. R. Okajima" <hooanon05@...oo.co.jp>
To:	Nick Piggin <npiggin@...nel.dk>
Cc:	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


Nick Piggin:
> It's not scaling but just single threaded performance. gcc turns memcmp
> into rep cmp, which has quite a long latency, so it's not appripriate
> for short strings.

Honestly speaking I doubt how this 'long *' approach is effective
(Of course it never means that your result (by 'char *') is doubtful).
But is the "rep cmp has quite a long latency" issue generic for all x86
architecture, or Westmere system specific?


J. R. Okajima
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