Re: Performance issue of 'git branch'

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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.
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