Author: Robert Hyatt
Date: 17:00:44 08/05/03
Go up one level in this thread
On August 05, 2003 at 19:13:21, Slater Wold wrote: >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. > >I really don't think it is a NUMA machine. > >"Advanced symmetric multiprocessing (SMP) up to 32-way", is how the exactly >describe it. > >And when you go to their 'Clusters' section, this machine isn't mentioned. NUMA is not necessarily a "cluster". There are several machines that are called "SMP" but also use a NUMA approach for memory. The clue is the price. A real 32-way shared memory system is _really_ expensive. Cray claimed that 50+% of the price of the T932 was in the memory interconnect to support full memory speed to all processors. Of course, I'm not wagering anything on this "hip shot" as to the idea behind the machine, but from what I have seen in past years, anything beyond 8 CPUS is either _way_ expensive, or NUMA.
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