Author: David Rasmussen
Date: 13:21:43 01/02/02
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On January 02, 2002 at 16:17:31, Robert Hyatt wrote: >On January 02, 2002 at 15:41:41, Peter Berger wrote: > >>On January 02, 2002 at 15:34:55, David Rasmussen wrote: >> >>>I've tried running Crafty at my universitys multiprocessor machines, with poor >>>results. Using 4 processors was kind of ok, but not great (~750 knps), but using >>>many more processors (16, 24, etc.) just made it slower. How crummy is that. >>> >>>/David >> >>Are you sure? Sparc processors usually scale very well. >> >>If it really became worse I'd suspect a problem with Crafty. > >No.. it is a problem with memory bandwidth. The sparc is too slow >and the crossbar is even slower... If you don't run out of the cache, >you get killed on memory bandwidth with large numbers of processors... > >> >>OK, a silly question: did you remember to recompile Crafty so that it really >>could use all those processors? > >That is a good point, with -DCPUS=128 or something similar... >Otherwise most processors will be spinning and eating bandwidth for >nothing... > > I did that already. I really don't understand how the Sparcs can be _that_ bad. I mean, they are used at my university for large mathematical problems using lots of RAM and processors, and they _do_ scale. Otherwise they wouldn't have bought such an expensive machine, let alone more than one of them. /David
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