From: Linus Torvalds <torvalds@osdl.org>
Date: Wed, 01 Feb 2006 01:04:00 GMT
Subject: Re: Bottlenecks in git merge
Message-ID: <Pine.LNX.4.64.0601311701000.7301@g5.osdl.org>
In-Reply-To: <20060201005035.GD31278@pasky.or.cz>



On Wed, 1 Feb 2006, Petr Baudis wrote:
> 
> xpasky@machine[0:0]~/linux-2.6.git$ echo -e '#!/bin/sh\n/bin/true' >r && chmod a+x r
> xpasky@machine[0:0]~/linux-2.6.git$ time git-merge-index -o ./r -a
> 
> real    0m3.827s
> user    0m1.788s
> sys     0m2.004s
> xpasky@machine[0:0]~/linux-2.6.git$ time git-merge-index -o ~/git-pb/git-merge-one-file -a
> [lots of "Removing"]
> 
> real    1m21.773s
> user    0m30.806s
> sys     0m13.248s
> 
> The costs are apparently in git-update-index, not in the shell.

Btw, this is where "oprofile" really shines. You can get exact listings of 
which symbols in which programs are taking up CPU-time, even when the time 
is spent in hundreds of different executions of a program.

Me, I'm too lazy to use it often, but not too lazy to point others towards 
it.

You do need to have kernel support for it compiled in, and it works better 
on certain CPU's (that have supported counters) than on others.

		Linus