Author: Matthew Hull
Date: 16:08:21 08/05/03
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On August 05, 2003 at 18:38:51, Robert Hyatt wrote: >On August 05, 2003 at 17:30:51, Matthew Hull wrote: > >>Does Crafty scale above 4 processors? For example, could crafty utilize all the >>CPUs on an IBM pSeries 690 7040-681T 32-way? >> >>http://www-132.ibm.com/content/home/store_IBMPublicUSA/en_US/eServer/pSeries/high_end/690.html >> >>MH > > >I didn't have time to look closely. But it is most likely a NUMA platform, >which means that Crafty as it exists now is not going to work well on it. NUMA >machines require careful attention to what is put where in memory, so that >often-used data is as close to the physical processor (in terms of access >latency) as possible. The current implementation of SMP in Crafty is based >on pure SMP, where memory is simply shared. > >If I ever have time to fiddle with a NUMA machine, I'll probably look at >fixing the major issue, which is to put split blocks close to each processor, >and when giving a specific processor a tree to search, using a split block that >is _close_ to it. Would the n-way speedups for NUMA be less than with a pure SMP? I.e. you would not see the 1.7-1.9 you get now on Xeons, but something less perhaps. I remember on IBM mainframes, there was a point of diminishing returns after about 10-way with 12-way being the limit. But that was a while back. Now they have 16-way machines that scale well on the Cheryl Watson benchmarks, but I don't know if they are pure SMP or not. I suppose NUMA does not have that problem (just different problems as you mentioned) since I see massively parrallel machines mentioned here abouts. MH
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