Author: Robert Hyatt
Date: 08:06:18 09/02/03
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On September 02, 2003 at 00:02:34, Jeremiah Penery wrote: >On September 01, 2003 at 23:39:13, Robert Hyatt wrote: > >>On August 29, 2003 at 18:32:46, Jeremiah Penery wrote: >> >>>Of course you can do a lot better - all I'm saying is that there's no way you're >>>going to be doing worse. >> >>I don't remember saying I would be doing worse. I remember saying I would >>be doing _bad_. Because potentially all memory references would be non-local. > >If you'd be doing "_bad_" in that case, how would you say you're doing now with >SMP, where _every_ access is *slower than worst case* on that Opteron machine? Somehow we are experiencing "a failure to communicate" (cool hand luke quote). My first port to the Cray resulted in a program that ran at 1K nodes per second in 1981. The previous machine was doing about 100 nodes per second, so that was a gain. On that same machine, 5-6 years later we were doing 20K nodes per second. I'd call 1K _BAD_. Even though it was faster than we had gone previously. But with a NUMA box, it is certainly possible to run +slower+ than before too. Just run on a 32-way box and put all important data in one CPU. If you think the Opteron is going to fly there, you are sadly mistaken. A crossbar is always better, if price is not considered. Any compromise to control price also limits performance.
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