Author: Robert Hyatt
Date: 20:23:18 09/01/03
Go up one level in this thread
On September 01, 2003 at 09:39:55, Jeremiah Penery wrote: >On September 01, 2003 at 06:09:48, Mridul Muralidharan wrote: > >>Hi Jeremiah, >> >> If you want crafty to get to work with a decent speedup on a 16 or 32 CPU >>cc-numa where you have say 2 - 4 processors per node with a significant >>inter-node latency (like most higher cpu numa boxes ?!) , you will have to >>ensure that the way you split , memory usage , etc is optimal - you dont want to >>access a hash entry in proc 0 from proc 32 when the latency wil be in >>milliseconds !!! > >The specific discussion was about Opteron machines up to 8 CPUs, which will all >be contained in one node and have extremely low non-local memory latency. > >Any large (multi-node) SMP machine will have the same problem as NUMA with >respect to inter-node latency. SMP doesn't magically make node-to-node >communication any faster. Actually it does. SMP means symmetric. NUMA is _not_ symmetric. Check out a Cray T932 with 32 processors, and a big crossbar. There is no NUMA-type latency issues there. All memory is directly accessed by each CPU with equal latency for _any_ word of memory for any processor... >But in reality, almost nobody uses a machine that big, especially for chess. >For any but the most extremely scalable architectures, there is significant >diminishing returns when adding processors for chess playing. I'd say that a >very scalable 8-way SMP or NUMA (Opteron) machine will not be very much slower >than even a 64-way Alpha/Itanium/xxx machine for chess.
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