Author: Robert Hyatt
Date: 20:40:19 09/01/03
Go up one level in this thread
On September 01, 2003 at 23:39:13, Robert Hyatt wrote: >On August 29, 2003 at 18:32:46, Jeremiah Penery wrote: > >>On August 29, 2003 at 08:46:12, Robert Hyatt wrote: >> >>>On August 28, 2003 at 19:12:52, Jeremiah Penery wrote: >>> >>>>But it's not more latency than you get *best case* when using a traditional SMP >>>>setup. So you can only gain, even with a "poor algorithm". >>> >>>If you compare an SMP xeon to a dual 486 you _also_ "win". >> >>And what is that supposed to demonstrate? > >That you can win with a poor algorithm, when the hardware is faster. >But you won't win anywhere near max theoretical "win". > >For a chess person, that's important. > >We work for 5% _all_ the time. > > >> >>>But my point was that with a NUMA architecture, you might win a lot less >>>than you could, if the algorithm doesn't take into account the specific >>>architectural issues with a NUMA machine. >>> >>>My point was, again, that you want most references from a CPU to go to its >>>local memory for max performance. It's an issue on _all_ NUMA-type machines. >> >>Of course I know that. My point is that with Opteron, even if you are accessing >>non-local memory *always*, you are not accessing it slower than you would with, >>say, a traditional SMP machine (2x Xeon, for instance). > > >OK.. Buy that F-1, but you don't get it into 6th gear. You will be fast. > >But you _could_ go a _lot_ faster... > >That was my point. > > > > >>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. > >> >>Either way you win, even with a crappy NUMA algorithm. > >As I said "if you call that winning..." Also, I don't think it is that clear. IE if you have 8 cpus, and 7 of them are beating on _one_ processor's local memory, you _will_ have problems. _serious_ problems. That can happen with the current crafty algorithm.
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