Author: Robert Hyatt
Date: 10:34:09 11/12/03
Go up one level in this thread
On November 12, 2003 at 13:18:48, Matthew Hull wrote: >On November 12, 2003 at 12:18:22, Anthony Cozzie wrote: > >>On November 12, 2003 at 11:55:20, Gian-Carlo Pascutto wrote: >> >>>On November 11, 2003 at 23:42:45, Eugene Nalimov wrote: >>> >>>>My point is: it's possible that due to the fact that quad Opteron is NUMA -- >not SMP -- system, for SMP-only program performance on quad Opteron can be >>>>worse than on *real* quad SMP system, even when for one CPU Opteron >>>>performance is much better. Itanium was used only as an example of such >>>>system, I never recommended rewriting any program for it. >>> >>>I don't understand how. The NUMA part is RAM. Even worst case on the Opteron >>>RAM is faster than Xeon SMP. So how could it ever be worse? >>> >>>-- >>>GCP >> >>Aaron's argument is: if a 1x opteron is faster than a 1x Xeon, a 4x opteron will >>be faster than a 4x Xeon. >> >>Nalimov is saying that Fritz may scale worse on the opteron due to NUMA issues. >>In other words, this is comparing latency with 1x opteron and NUMA opteron >>relative to 1x Xeon vs SMP Xeon. >> >>Off hand this seems logical to me . . . > >Perhaps Eugene can tell us if SMP crafty was slower on 2x opteron than Bob's 2x >Xeon, before the NUMA mods were made? > >MH Yes. It was _really_ bad on the opteron. But then again it was also not real good on my xeon. Even though the NPS scaled _perfectly_ on my older quad xeons. The PIV went to a longer cache line, which caused some coherency overhead that hurt. This has been addressed in the current code. But the problem was worse on the opteron due to the NUMA delays, compared to the PIV xeons which simply have a longer cache line to aggravate the problem. > >> >>anthony
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