From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Wed, 07 Oct 2009 22:28:14 GMT
Subject: Re: [PATCH] Add the --submodule-summary option to the diff option family
Message-ID: <alpine.DEB.1.00.0910080027270.4985@pacific.mpi-cbg.de>
In-Reply-To: <7vd44zt1nf.fsf@alter.siamese.dyndns.org>

Hi,

On Wed, 7 Oct 2009, Junio C Hamano wrote:

> Jens Lehmann <Jens.Lehmann@web.de> writes:
> 
> > So i took a live repo from my dayjob containing 8 submodules. In each
> > submodule i did a "git checkout HEAD^" to simulate one change.
> 
> It appears that your "simulation" is to have changes in all submodules 
> and nowhere else in the tree.  I have to wonder how common would that 
> be.  If I have been working in the subprojects without changing the 
> superproject at all, I would likely to be in one of the subproject 
> directories and my "git diff" would not even have to trigger this 
> codepath.  If we have on the other hand changes in the superproject, 
> showing them would cost us equally in both approaches.
> 
> > then i got:
> >
> >   without fork : real	0m0.203s
> >   with fork    : real	0m0.453s
> >
> > This is a degradation of more than 120% because of the fork()s. And
> > just for fun i ran the scripted submodule summary too:
> >
> >   scripted     : real	0m3.437s
> >
> > So the forked version outperforms the scripted version by a factor of
> > 7, while the speedup from Dscho's original proposal is almost 17fold.
> 
> Thanks.  I was worried if the forking to ensure correctness may sactifice
> performance so much to be unusable, but it does not seem to be the case,
> given the above comparision.
> 
> I didn't look at the code but presumably it uses the run_command()
> interface and cleanly written?

You seem to be rather unconvinced by rather convincing numbers.

Therefore, I will continue working on the --submodule-summary stuff in 
4msysgit.git.

Ciao,
Dscho