Author: Robert Hyatt
Date: 10:29:02 09/03/03
Go up one level in this thread
On September 03, 2003 at 13:12:34, Gian-Carlo Pascutto wrote: >On September 03, 2003 at 12:05:43, Robert Hyatt wrote: > >>>As I've said, there's nothing that magically makes SMP *inherently* faster >>>than NUMA. Nothing more. >> >> >>That's not what I said. SMP _is_ inherently faster. Because all memory has >>the same access latency. You _do_ have to share _something_ in a parallel >>algorithm. ANd whatever that is will be slower than doing the same thing on >>a SMP box. Even if it is just one word, the SMP box will access that one >>word faster all around and the program will run faster. >> >>Perhaps not a lot faster for 1 word of shared data. But faster nonetheless. > >I don't understand. > >Even the slowest access on a NUMA Opeteron is twice as fast as on a SMP >Xeon. > >How can it be slower then? You keep changing the subject. I am not comparing apples to oranges. I am comparing two machines that are _identical_ in every way except one has a pure SMP memory interconnection while the other has a pure NUMA interconnection. No references to X86 vs Opteron. No references to Cray vs Sun. If you give me two boxes that are identical except for SMP vs NUMA, the SMP box will _always_ have a speed advantage. It might not be much for small numbers of processors, but it _will_ be there. But if you want to compare opteron NUMA to something else, I'll take a Cray T932 which is a pure crossbar SMP machine. Want to compare latencies there? The Cray is _always_ 120 ns. No matter what part of memory from which processor you access. However, that is just as unfair as opteron to X86. NUMA is worse, period, when compared to an equivalent non-NUMA machine, in all respects _but_ pricing. That is where NUMA shines, and it is why NUMA was developed in the first place. NUMA was _not_ a solution to a performance problem. It was a solution to a _pricing_ problem. The Crossbar was a solution to a performance problem. > >-- >GCP
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.