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Re: FW: [Bug-gnubg] Simple multi-threading... Cache

From: Jonathan Kinsey
Subject: Re: FW: [Bug-gnubg] Simple multi-threading... Cache
Date: Wed, 24 Jan 2007 16:45:24 +0000
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv: Gecko/20061207 Thunderbird/ Mnenhy/

Øystein Johansen wrote:
> Jonathan Kinsey wrote:
>> The current cache has a simple "two slot" approach, in that if a hash
>> clashes the old hit is put in a back up slot; furthermore if the 2nd
>> slot is hit then it's swapped with the 1st.
> I haven't browsed the cache code much, this sounds more like a cuckoo
> scheme to me.

It's fine, hash functions often have collisions and storing more than
one entry at a hash is normal.

I've tested the single slot approach and it's 5-10% worse, which is
bad...  So even though there's twice the number of slots the hash
function isn't perfect.  It suggests to me that using 3 or 4 slots per
hash might be better.  Or we need to alter the hash function to improve
the spread, although it looks fine at a quick glance and these things
are tricky to adjust.

It's looking like we may have to have a cache per thread after all, I
wonder how many duplicate evaluations this will involve - quite a few
I'd think...


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