Re: Some git performance measurements..

From: Joachim B Haga <cjhaga@fys.uio.no>
Date: Dec 1, 2007, 11:36 UTC
Message-ID: <85abou8x5n.fsf@lupus.ig3.net>
In-Reply-To: <alpine.LFD.0.9999.0711281852160.8458@woody.linux-foundation.org>

Linus Torvalds <torvalds@linux-foundation.org> writes:

> The pack-files (both index and data) are accessed somewhat randomly, but 
> there is still enough locality that doing read-ahead and clustering really 
> does help.

They are dense enough that slurping them in whole is 20% faster, at least here. And much less noisy! These are both cache-cold tests.

$ time git read-tree -m -u HEAD HEAD

real 0m9.255s user 0m0.832s sys 0m0.196s

$ time (cat .git/objects/pack/* .git/index >/dev/null; git read-tree -m -u HEAD HEAD)

real 0m7.141s user 0m0.936s sys 0m1.912s

Now, I don't know how useful this is since git doesn't know if the data are cached. Is it perhaps possible to give a hint to the readahead logic that it should try to read as far as possible?

-j.