Re: What's cooking in git.git (topics)

From: David Kastrup <dak@gnu.org>
Date: Sep 27, 2007, 06:08 UTC
Message-ID: <854phgfxn7.fsf@lola.goethe.zz>
In-Reply-To: <20070927023633.GA28902@coredump.intra.peff.net>

Jeff King <peff@peff.net> writes:

Show 10 quoted lines

> On Wed, Sep 26, 2007 at 01:05:59PM -0700, Junio C Hamano wrote:
>
>> * jk/diff-rename (Tue Sep 25 15:29:42 2007 -0400) 1 commit
>>  + diffcore-rename: cache file deltas
>> 
>> Parked in 'next' for now but is 'master' material.
>
> My tests after this patch show that spanhash_find is responsible for
> a large portion of the processing time in large renames, so I am going
> to look into speeding that up.

In itself, it does not look like there is all too much room for optimization. One can remove the temporary pointer "optimization" and see whether this makes strength reduction possible for the compiler. Making this an endless loop wrapped around a loop on bucket might also help the compiler in that effect.

But there is really not all too much leeway, and it might be better spent in the caller. For example, the search will take something like r/(1-r) iterations on average where r is the fill ratio of the hash array. So one would not want to, say, let r grow above 0.75 or something like that.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum