Author: Dave Gomboc
Date: 19:51:22 07/20/99
Go up one level in this thread
On July 20, 1999 at 22:04:42, Don Dailey wrote: >On July 20, 1999 at 17:31:44, Dan Homan wrote: > >>On July 20, 1999 at 15:19:52, Don Dailey wrote: >> >>>On July 20, 1999 at 00:45:58, hgkjhg wrote: >>> >>>>Don, is Cilkchess going to be released as a commersial or freeware program some >>>>time? >>> >>>I thought about releasing Occam when it gets good. But I don't want >>>to see 10000 occams on the chess server or at tournaments! I may release >>>a version before it gets too strong perhaps just an executable for linux >>>and windows. >>> >>>Probably there will be a parallel version of Occam that will be released >>>with the Cilk distribution as an example with source code. Cilk is free >>>and so would this be. But I don't know if I would release a really >>>advanced version. You will be surprised how simple it is to write a >>>parallel chess program when you see this. >>> >>>- Don >> >>Don, >> >>I was looking over the Cilk Pousse web page and it was pretty clear from >>this how to use Cilk to write a parallel chess program with minimal >>effort, but I had a question: Do you need to have local data structures >>(position, move list) at each node? It seemed to me (as I read the >>web page) that you would. My assumption is that this would create >>substantial overhead that would be a problem for non-parallel versions >>of the program. >> >>Second question: Can cilk be compiled and used with C++ or does it require >>pure ANSI C? >> >> - Dan > >This is a question everyone asks. We do it this way because it works >very well and is clean. But it's not necessary. In any parallel >program you will have to create separate state in order to perform >your parallelism. Obviously you cannot have 256 processors updating >the same exact data structure right? But how you accomplish this >is solely up to you. > >In Cilkchess I choose to make it part of the search to simply make >a move by creating a brand new board and search state. This is >simple and fast. No one ever believes me when I tell them it's >fast but modern processors do memory block copies very rapidly, >it's just not a problem. Believe me when I say it's dwarfed by >the other complexities of making a move. If this is a problem >for you, you can always simply do the end nodes in place like in >a serial chess program and not do the state copy. But I'm telling >you that this is not necessary. Even in a serial chess program you >have to carry some state around, for instance all the undo information. >I don't carry any undo information because I don't ever unmake moves, >each position is sitting on the stack. Also I don't have any other >undo overheads either. > >Occam uses the same state copy and update technique all the way through >the quies search. Occam is my new chess program which is doing over >400,000 nodes per second on a pentium 500 in middlegame positions. >State copy is simply not expensive. It makes the whole chess program >a whole lot cleaner too, so it should appeal to meticulous programmers. > >If you read the web page about our cilk-pousse program we competed >and beat every other pousse program using these techniques. Every >cilk program is also a serial program and in private tests against >one of the other top 4 finishers we beat them with our serial version, >which is superfast. > >The move list I also put on the stack, declared as an array at the >top of the search function. If you wanted to, you could easily make >this a list but again, you have to solve the problem of different >processors accessing the same stack. It would be a simple matter >to do it differently depending on whether you are compiling the >serial or parallel versions, your move list is a pointer and an >ifdef determines whether to declare it or to point it to the right >place on your global list. > >As for your second question, cilk actually requires gcc right now. >It uses special features of gcc so you have no other options. You >can link in from other compilers as long as you do the searh part >in gcc. We are looking at making cilk more compiler portable but >this is a way off. Sorry. But there is nothing wrong with Gcc, >there are some great versions with strong pentium optimizations >that are as good as any compiler (please no holy wars over this) >as far as performance. > >- Don I've tried using Cilk, I think it's pretty good. I wish it would work with g++ though. Dave
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