Re: Performance issue of 'git branch'

On Wed 22.Jul'09 at 21:10:49 -0700, Linus Torvalds wrote:

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.

GIT_USE_LOOKUP=1 makes is a bit slower overall. 

Without your patch, I get fewer pagefaults (1254 vs 1404) when
it is set, but it takes ~0.5s longer (it varies a bit).

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.

With your patch and GIT_USE_LOOKUP=1 I get 751 pagefaults, versus 775
if GIT_USE_LOOKUP is unset, but it is faster when unset.

So your patch without GIT_USE_LOOKUP=1 is the fastest option.