[ccache] Questions about two hot functions in ccache

Justin Lebar jlebar at mozilla.com
Tue Oct 19 19:02:11 MDT 2010

> Indeed. (This was by the way mentioned on the list a couple of weeks
> ago: http://www.mail-archive.com/ccache@lists.samba.org/msg00532.html)

To respond to Ramiro in that thread:

> Joel, is there a way we can time how long each part of ccache takes?

You can probably use xperf on Windows.

> Do you want to work on this? That would be awesome! I currently don't
> have much ccache time, and when I get some, I would like to work on
> other things first.

I have a few other projects to finish first, but I'll definitely add
this to my (short, but non-empty) list of toolchain patches to write.
It looks like there's serious performance to gain here.

> Even the 64-bit version of murmurhash has way too high
> collision rate.

Ah, I didn't realize that murmurhash gave a single word as output.
Yes, that's no good.

> MD4 has been there from the start and neither Tridge or I have seen any
> reason to switch it. MD5, SHA1 and other even more modern cryptograhic
> hash functions are indeed stronger but also slower, and the increased
> resistance against various crypto attacks doesn't seem necessary in a
> tool like ccache.

I'm also no expert on hash functions, but I'll e-mail around.


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