Re: [PATCH] xdiff: optimise for no whitespace difference when ignoring whitespace.

From: Dylan Reid <dgreid@gmail.com>
Date: Jul 6, 2010, 03:04 UTC
Message-ID: <AANLkTilkML1edHz6JSj7w3u60oFt3Va-5Z2ZBWVphxVI@mail.gmail.com>
In-Reply-To: <7vsk3x72wb.fsf@alter.siamese.dyndns.org>

On Mon, Jul 5, 2010 at 10:36 PM, Junio C Hamano <gitster@pobox.com> wrote:

Show 6 quoted lines

> Dylan Reid <dgreid@gmail.com> writes:
>
>> In xdl_recmatch, do the memcmp to check if the two lines are equal before
>> checking if whitespace flags are set.  If the lines are identicle, then
>
> "identical"?

That's exaclty what I meant.  Correct patch sent.

Show 8 quoted lines

>
>> there is no need to check if they differ only in whitespace.
>> This makes the common case (there is no whitespace difference) faster.
>> It costs the case where lines are the same length and contain
>> whitespace differences, but the common case is more than 20% faster.
>
> "more than 20% faster" based on what dataset and benchmark?
>

I benchmarked it with some of the bigger files from Linux. The results were consistenly > 20% faster across different file sizes. I tested it by simply running the command a few times then running it with my local build a few times to see if I had achieved any speedup.

~/linux-2.6(119)$ time git blame --incremental -w ./sound/pci/hda/patch_realtek.c > /dev/null

real 0m8.166s user 0m8.063s sys 0m0.090s ~/linux-2.6(120)$ time git blame --incremental -w ./sound/pci/hda/patch_realtek.c > /dev/null

real 0m8.010s user 0m7.866s sys 0m0.137s ~/linux-2.6(121)$ time ~/work/git/git blame --incremental -w ./sound/pci/hda/patch_realtek.c > /dev/null

real 0m6.115s user 0m5.986s sys 0m0.123s ~/linux-2.6(122)$ time ~/work/git/git blame --incremental -w ./sound/pci/hda/patch_realtek.c > /dev/null

real 0m6.119s user 0m5.986s sys 0m0.127s

Thanks for taking the time to read the patch.

Dylan