Author: Vincent Diepeveen
Date: 19:44:51 09/15/01
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On September 15, 2001 at 22:29:57, Robert Hyatt wrote: >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). but you are sending a byte or 2? How about a chessprogram that's communicating with all bandwidth used up, try that and start horrorring! >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. Clan? $$$$ for each network card and $$$$$ for each switch? > >>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. I doubt the 'pretty common'. I never got any system time on such a network so far and the 'big networks' still have huge latencies and it is very uncommon that they have over 100mbit network cards. I'm not speaking for the US here of course, can't judge things over there. > > >> 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. Please don't compare a $0.001 program with nowadays strong chess programs. Get *any* speedup with crafty over a 10mbit network at 256 nodes and i'll believe you! If you get over the square root speedup for crafty out of 256 node 10mbit network you'll earn a nobel prize for sure! Of course crafty compared with the normal crafty that's running on a single cpu K7. Not the special network crafty at 1 processor compared to the speed of the 256 node crafty. Because this is exactly the problem. Jonathans search depths and the program that he uses to get it is anything but impressive. >>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. With a 100 mbit network with crafty you'll not even get close to 1.7 Best regards, Vincent
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