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

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Message-ID: <AANLkTinZuGdZ4BMipbeLQH4e6UQ6qVNDCYeOxMpg7+og@mail.gmail.com>
Date:	Tue, 14 Dec 2010 23:12:08 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Nick Piggin <npiggin@...nel.dk>
Cc:	Américo Wang <xiyou.wangcong@...il.com>,
	Nick Piggin <npiggin@...il.com>,
	"J. R. Okajima" <hooanon05@...oo.co.jp>,
	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 Tue, Dec 14, 2010 at 9:54 PM, Nick Piggin <npiggin@...nel.dk> wrote:
>
> That's what I would like to know, but I suspect that for very short
> strings we are dealing with, the custom loop will be fine for
> everybody.

Yeah, I can pretty much guarantee it for the common case of short
strings. Most path components are short enough that a "clever"
memcmp() is simply likely going to be slower than doing things
byte-per-byte.

That's especially true if we then in the future end up making it do a
long-by-long compare instead of the byte-by-byte one.

                        Linus
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