Re: Performance issue of 'git branch'

On Wed, 22 Jul 2009, Linus Torvalds wrote:

But I'll see if I can dig up my non-binary-search patch and see if I can 
make it go faster. My machine is fast, but not so fast that I can't 
measure it ;)

Oh. We actually merged a fixed version of it. I'd completely forgotten.
 
Enabled with 'GIT_USE_LOOKUP'. But it seems to give worse performance, 
despite giving me fewer searches: I get 2121 probes with binary searching, 
but only 1325 with the newton-raphson method (for the non-fixed 'git 
branch' case).

Using GIT_USE_LOOKUP actually results in fewer pagefaults (1391 vs 1473), 
but it's still slower. Interesting. Carlos, try it on your machine (just 
do

	export GIT_USE_LOOKUP=1
	time git branch

to try it, and 'unset GIT_USE_LOOKUP' to disable it.

(And note that the "=1" part isn't important - the only thing that matters 
is whether the environment variable is set or not - setting it to '0' will 
_not_ disable it, you need to 'unset' it).

With my fix to 'git branch', it doesn't matter. I get the same 
performance, and same number of page faults (676) regardless. So my patch 
makes the GIT_USE_LOOKUP=1 thing irrelevant.

		Linus