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

From: Shawn O. Pearce <spearce@spearce.org>
Date: Jan 12, 2007, 06:26 UTC
Message-ID: <20070112062644.GC24195@spearce.org>
In-Reply-To: <7vr6u0wz2s.fsf@assigned-by-dhcp.cox.net>

Junio C Hamano <junkio@cox.net> wrote:

Show 11 quoted lines

> With the tip of linux-2.6 repository, v1.4.4 series takes 0.03s
> while v1.5.0-rc1 takes about 3.6s.  That is 100x fold, not just
> 4x.
> 
> It turns out that to describe 0404f87f (tip of linux-2.6) the
> new one picks up 61 tags in the posible-tag loop.
> 
> Since this loop uses the usual date-order, we can limit the
> number of candidate tags without losing too much precision.
> When limiting the candidates to only 6 (attached patch), the
> time drops to 0.25s.

OK. Apply your patch to master. 3.6s is insane, even for git-describe. I think your guess of 6 is reasonable, but I'd obviously like to remove the need for it entirely.

I think I have a sketch in my head for an algorithm that can compute the revision counts while in the possible-tag loop, which would completely remove the huge cost of the per-tag revision list later on. I can't work on it right now (need to get other stuff done before 1 pm Friday) but I will try to code and test it tomorrow afternoon. If I'm right I'll send a patch.

-- 
Shawn.