Re: [PATCH] grep: do not do external grep on skip-worktree entries

[Linus Torvalds <torvalds@linux-foundation.org>]

On Mon, 11 Jan 2010, Fredrik Kuivinen wrote:
> 
> Another option is to use memmem instead. As we know the length of the
> buffer already it should be a slight improvement over strstr for
> everyone. memmem may cause some portability problems though as it is a
> GNU extension.

I'd almost prefer to just drop the strstr entirely.

It's not actually all *that* big a win, even on my machine. I get

 - strstr:

        real    0m0.309s
        user    0m0.168s
        sys     0m0.136s

 - regexec:

	real	0m0.410s
	user	0m0.220s
	sys	0m0.116s

so yeah, it's slower, but not by a huge degree. With strstr, "git grep" 
actually beats the external grep for me, but I don't really care. It's 
already way better than it used to be - and clearly strstr has a lot of 
potential problems.

Sure memmem() might be better for you than strstr, but on the other hand, 
it might easily be worse than strstr for others - and not just from a 
portability standpoint. Is memmem() optimized to take advantage of SSE4.2? 
I suspect it is not, exactly _because_ it's a GNU extension, so Intel 
hasn't published optimized sample code for people to use.

So I would argue against even bothering to try memmem. Especially since	in 
your case, regexec() is apparently faster than memmem _anyway_. I expect 
that it is for me too, but I'm too lazy to check.

			Linus