Author: Sune Fischer
Date: 14:36:22 08/25/03
Go up one level in this thread
On August 25, 2003 at 17:28:33, Robert Hyatt wrote: >On August 25, 2003 at 16:28:31, Sune Fischer wrote: > >>On August 25, 2003 at 16:17:34, Dan Andersson wrote: >> >>> I would rather have 2.4 MNps on a single CPU :) And a single agent search will >>>be more efficient except special cases. A pardox is that larger cache can be >>>counter productive for some parallel applications due to increased memory >>>traffic. >> >>Yes, but this memory trafic is a different animal than what the thread was >>talking about. >> >>The tread was about making/uncopying, and for that you don't need inter chip >>communication, each thread can run independently and can uncopy independently on >>its own stack. For this double cache bandwidth is good, two chips can simply >>copy double as fast as one chips so Bob's argument that 2.4 Mnps was more than >>twice as bad 1 Mnps isn't valid concerning this specific issue. > >That is simply incorrect. > >Whether you have a dual or a single, if you run at 2.4M nodes per second >you have a definite cache bandwidth requirement, and a definite memory >bandwidth requirement, for my particular program, running at that particular >NPS. > >IE if I can run at 2.4M nodes per second on a _single_ CPU, I _still_ have >to copy _exactly_ the same number of bytes per node per copy/make. If I >do them 1/2 as fast, but do them twice on two processors at the same time >does not matter. The total bandwidth to support 2.4M nodes per second is >a fixed number whether I do it with 1 processor or 1024. Bob please. You compared 2.4 Mnps to 1 Mnps but you _can't_, such a comparison doesn't make sense. If you are going to go 2.4 on _one_ cpu that cpu most likely will be 2.4 times as fast and therefore have 2.4 times the cache bandwidth, so nothing changes with respect to uncopying. Yes you would need to copy 2.4 times as much, but you would also have an equivalently larger bandwidth, status que! You made it sound like 2.4 was much worse than 1, which is just a silly comparison at best. Fact of the matter is 2.4 is worse than 1 because it takes place on a _dual_, and that is the critical point I believe. -S.
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