Author: Robert Hyatt
Date: 19:29:57 09/15/01
Go up one level in this thread
On September 15, 2001 at 16:31:07, Vincent Diepeveen wrote: >On September 14, 2001 at 22:56:06, Pham Minh Tri wrote: > >>I see that dual computers are expensive, not easy to own and still limited in >>power of computing. >> >>I wonder how good / possible if we use all computers in a LAN for chess >>computing. LANs are very popular and the numbers of computers could be hundreds. > >LAN 1Gigabit /s or a slow 100mbit LAN? > >>Even though a LAN is not effective as a dual circuit, but the bigger number of >>processors could help and break the limit. >>What do you think? > >the problem is the hard work to make it. I had done some tests and have >a version of diep that nearly worked over the lan, but then i was confronted >with some huge slowdowns. Then i talked to Bob and i knew why. > >note that 100mbit networks aren't 100mbit networks really. Even the fastest >cards i could not get more than 60mbit through a second. > >a major problem is that if you try to get read info from it in a multithreaded >way that you get huge delays. Also multiprocessor the problem is exactly as >big. > >Before you receive info over the network you are already hundreds of >milliseconds further. This is a major problem. > I don't see that kind of speed on 100mbit switched networks. I don't even see 10ms delays there. And I have actually seen real speeds in the 1-5ms range to send a single packet from any two non-conflicting nodes (using a switch, ie). Of course there are faster ways to do this, by reducing the latency. Clan is one answer there. The latency can be dropped to the sub-microsecond range with no problems. >So a) you have huge overhead > b) you cannot communicate much > c) you will not be able to get systemtime on a big 100mbit network anyway. > d) the bigger the network the more chanceless you get a speedup at a > 100mbit network. "big networks" are pretty common now. If by "big" you mean "switched" rather than a "hub" network. We don't have any non-switched networks in our department now, since switches are cheap. > e) where at networks with nodes being dual or quad getting a speedup is > already hard, at networks where nodes are single cpu getting a positive > speedup is nearly impossible. I wouldn't go that far. Jonathan did pretty well several years ago using 10mbit non-switched (thickwire) ethernet. It obviously is not as fast as SMP machines, but it is better than nothing. > >I asked here some time ago for some volunteers and only got a few responses. >Regrettably the mailing list didn't work anymore so i lost most email >adresses, also not a single one has dual or quad machines. Getting a speedup >from a network 100mbit with single cpu nodes is nearly impossible for >an efficient program. > >Of course for the nodes a second it might look great, but that's not my >goal. > >So in short you CAN get a huge nps but if you measure speedup in the depth >you get at a dual versus a 8 node single cpu, then you will be hugely >dissappointed. The dual will outgun the 8 node anywhere if it's a 100mbit >network. I wouldn't bet on that myself, if the dual cpus are the same speed as the 8 networked cpus. It will take some work, but getting 4x faster would not be anywhere near impossible.
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