Author: Robert Hyatt
Date: 06:44:37 09/16/01
Go up one level in this thread
On September 15, 2001 at 22:48:41, Vincent Diepeveen wrote: >On September 15, 2001 at 22:34:27, Robert Hyatt wrote: > >>On September 15, 2001 at 03:28:18, Tony Werten 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. >>>>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? >>> >>>When you search a chesstree, a lot of times you come into parts of tree that you >>>have searched before. You either don't want to search this part again ( you have >>>searched it deep enough before ) or you want to have the best move from the >>>previous search. Hashtables do exactly this. >>> >>>In a LAN (or a cluster) you don't share this hashtable and therefor are >>>searching the same tree (or parts of it ) time and time again. If you count the >>>number of nodes searched per second it's a linear speedup but effectively it's >>>useless. You have to add a lot of computers before you get any real speedup, >>>specially in the endgame. >>> >>>cheers, >>> >>>Tony >> >> >>This is not necessarily true. Several programs have distributed the hash table >>across network nodes. It requires small changes to the basic search algorithm, >>but a distributed hash table is not only doable, it has been done more than >>once. >> >>I will probably do this in the distributed Crafty when I do it... > >At a 100mbit network i tried to ship 16 bytes packet as fast as possible >from a node to another node. > >I managed to do that with a CROSS-UTP cable about 3000 times a second. > >That means in short that without counting the 60ms receiving delay in linux, >30ms in windows or something, that you can only ship and get a hashtable >entry at 1500 times a second. There is no 60 ms delay in linux. I run this test all the time. And I can sustain 80 megabytes per second with no trouble at all using a C program and a tcp/ip stream protocol. You should also check your math. 50ms would mean 20 packets per second, which is ridiculous. 1ms means 1000 packets per second which is always doable. > >so unless you want to create a deep blue crafty where you only hash the >first so many plies, then you sure will slow down crafty a factor of say >450? > Hashing the first N plies may well be an idea. I already don't hash the q-search. I believe Junior doesn't hash the last non-qsearch ply. It seems to work ok for us... >How big is your cluster then to get a speedup of over 1.0 ?
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