Author: Vincent Diepeveen
Date: 07:09:06 01/03/02
Go up one level in this thread
On January 02, 2002 at 23:06:29, Robert Hyatt wrote: >On January 02, 2002 at 16:21:43, David Rasmussen wrote: > >>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 > > >It is almost certainly a horrible MUTEX implementation. POSIX threads does >terribly on Linux if I have to use the normal MUTEX (pthread_lock()) stuff. >The spinlocks I use make everything work. Although since I no longer have to >lock the hash stuff, there are not a lot of locks left in Crafty so this might >not be true as I haven't tested it in a long while... Don't complain about that only, modify the splitting i'd say. Split less near the leafs :) Note that you don't lock hashtable which would give some rights to complain :)
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