From: Marco Costalba <mcostalba@gmail.com>
Date: Sat, 25 Mar 2006 09:35:39 GMT
Subject: Re: Use a *real* built-in diff generator
Message-ID: <e5bfff550603250135h42b0da62x84973483798d969c@mail.gmail.com>
In-Reply-To: <Pine.LNX.4.64.0603241938510.15714@g5.osdl.org>

On 3/25/06, Linus Torvalds <torvalds@osdl.org> wrote:
>
> This uses a simplified libxdiff setup to generate unified diffs _without_
> doing  fork/execve of GNU "diff".
>
> This has several huge advantages, for example:
>
> Before:
>
>         [torvalds@g5 linux]$ time git diff v2.6.16.. > /dev/null
>
>         real    0m24.818s
>         user    0m13.332s
>         sys     0m8.664s
>
> After:
>
>         [torvalds@g5 linux]$ time git diff v2.6.16.. > /dev/null
>
>         real    0m4.563s
>         user    0m2.944s
>         sys     0m1.580s
>

Currently 'getting the diffs' is the second most important time
consumer  of annotation calculation (just after getting the file
history). On big and heavily modified files, as drivers/net/tg3.c in
Linux tree, this can be very slow (around 10s on my box).

The profiling has been done on qgit, but I think  it is of general
interest because qgit uses git-rev-list and git-diff-tree -p to get
file's history and diffs respectively.

So this patch is more then welcomed!  Thanks!

Marco