Author: Robert Hyatt
Date: 06:37:50 09/16/01
Go up one level in this thread
On September 15, 2001 at 22:44:51, Vincent Diepeveen wrote: >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? No... try writing some code. One of the things I have kids do in my network programming course is to answer just that question. And it turns out that the size of the packet is _far_ less important than the number of packets sent. IE sending one 1K packet is almost 10x faster than sending 10 100-byte packets. > >How about a chessprogram that's communicating with all bandwidth used up, >try that and start horrorring! When you are out of bandwidth, you are just out of bandwidth. But in Linux, I can sustain about 80 mbits/second on 100mbit ethernet using a switch. You simply have to write the algorithm with the bandwidth limit in mind. > >>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? At the moment. However, the price is coming down. > >> >>>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'. Not sure what you mean, but I haven't seen a "dumb hub" in a couple of years. Here at UAB. At public K-12 schools. Where my wife works. Etc. Why would anyone buy a dumb hub when a switched 8-port device is so cheap? > >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. 1-2ms latency is reachable on 100mbit networks. That isn't horrible and can be lived with. > >> >> >>> 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. Then please don't assume that "If I can't do it it can't be done". It was done 15 years ago on non-switched 10mbit ethernet. It can be done _better_ today on 100mbit or gigabit switched ethernet. > >Get *any* speedup with crafty over a 10mbit network at 256 nodes >and i'll believe you! I don't have any 10mbit networks. But I will get a speedup on a 100mbit network before too long. > >If you get over the square root speedup for crafty >out of 256 node 10mbit network you'll earn a nobel >prize for sure! This has already been done. > >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. The "special network" crafty will be exactly the same when only using one node. Just like I don't lose a thing with the SMP crafty if it uses just one processor. > >Jonathans search depths and the program that he uses to >get it is anything but impressive. So? He didn't use null-move with R=2 or R=3, he didn't use it recursively. That would put him right back in line with today's programs. > >>>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 Care to make a wager? I'll guarantee you you will lose. But it is your money to throw away.. > >Best regards, >Vincent
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