Author: Robert Hyatt
Date: 13:02:32 08/23/05
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On August 23, 2005 at 10:25:36, Joachim Rang wrote: >On August 23, 2005 at 06:18:31, A. Cozzie wrote: > >>Zappa is not really that great at blitz. In fact before the WCCC I did a test >>at 5+0 vs Fruit and Fruit won 75% - and I was using 2 processors for Zappa. >> >>However at 15+5 that score was reversed (of course I was still cheating there :) >> >>The reason is that Zappa concentrates on getting a deep search by an efficient >>branching factor, not pruning/big nps, so it needs some time before it begins to >>outsearch opponents. It is a serious chess engine, not a blitzer. >> >>anthony > >Bob stated in some posts that a parallel search needs some time to "stabilize" >which means it can be weaker in blitz. Do you think this is related to your >phenomenon? Was it a joke that Fruit got 75% in 5+0 but only 5% in 15+5? I can't >imagine such a difference. > >regards Joachim My weaker blitz performance this year was a different issue. I play blitz all the time on ICC. But for the new dual-core opteron, I had to tune the parallel search to split less often (greater distance from the leaf positions) to reduce memory bandwidth. The dual-cores have a bit of a bottleneck there compared to the single-core opterons I have used in the past. Each dual core chip has two L1 and two L2 caches, but just one hypertransport interface and one memory controller. The hypertranspost handles a _lot_ of cache-to-cache traffic, and with two cpus, it sees 2x the traffic a single-core processor sees. Ditto for the memory controller. As a result, I had to tune things to do fewer splits (which is a high bandwidth operation). But that hurts blitz trees. For example, at the WCCC, I didn't split within 6 plies of a leaf position. Searching 15-16 plies, that worked extremely well and parallel performance was good. But in very fast blitz games, where I might only get to search 10 plies deep in a .1 second search, suddenly the extra processors are not helping that much...
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