Re: gc --aggressive

From: Nicolas Pitre <nico@fluxnic.net>
Date: May 1, 2012, 17:59 UTC
Message-ID: <alpine.LFD.2.02.1205011348090.21030@xanadu.home>
In-Reply-To: <20120501171640.GA16623@sigill.intra.peff.net>

On Tue, 1 May 2012, Jeff King wrote:

Show 20 quoted lines

> On Tue, May 01, 2012 at 12:28:06PM -0400, Jeff King wrote:
> 
> > >  You could test this theory by commenting out the size comparisons in 
> > > type_size_sort() and re-run the test.
> > 
> > I'll try this next.
> 
> Wow, it behaves horribly. I didn't even let the bigger tests run to
> completion. Here is the output for git.git (the first line is from the
> original, unmodified version of git with --window=10):
> 
>   orig | 31.4M (100%) |   54s (100%)
>     10 | 44.0M (140%) |  169s (310%)
>     20 | 37.7M (120%) |  232s (428%)
>     40 | 33.6M (107%) |  331s (608%)
>     80 | 30.9M ( 99%) |  473s (868%)
>    160 | 29.4M ( 94%) |  696s (1279%)
> 
> Unless the window is increased a lot, the packs end up quite a bit
> larger (and even still we spend a lot more CPU time).

Bleh.  Allright.

One final quick test if you feel like it: I've never been sure that the last comparison in type_size_sort() is correct. Maybe it should be the other way around. Currently it reads:

	return a < b ? -1 : (a > b);

While keeping the size comparison commented out, you could try to replace this line with:

	return b < a ? -1 : (b > a);

If this doesn't improve things then it would be clear that this avenue should be abandoned.

Nicolas