Author: Keith Evans
Date: 10:29:36 06/20/02
Go up one level in this thread
On June 20, 2002 at 13:03:10, Robert Hyatt wrote: >On June 20, 2002 at 12:30:47, Keith Evans wrote: > >>On June 19, 2002 at 23:27:51, Robert Hyatt wrote: >> >>>On June 19, 2002 at 20:45:33, Keith Evans wrote: >>> >>>>On June 19, 2002 at 14:33:56, Tom Kerrigan wrote: >>>> >>>>>On June 19, 2002 at 13:10:42, Robert Hyatt wrote: >>>>> >>>>>>I don't care about the 32 bit specint. I care about the fact that a >>>>>>1.4ghz pentium runs Crafty at about 750K nodes per second. The 600mhz >>>>>>21264 ran it at over 800K. And 600mhz is _not_ the fastest 21264 around. >>>>>> >>>>>>The 1ghz mckinley runs it twice as fast as that 1.4ghz pentium, 1.5M nodes >>>>>>per second. _that_ is definitely "something to get excited about" IMHO.. >>>>> >>>>>So you like the 21264 and the McKinley. That's great. Maybe you can start a fan >>>>>club, instead of posting to a thread where people are trying to have an >>>>>intelligent conversation about 64-bit computing. >>>>> >>>>>-Tom >>>> >>>>Is there an easy way to compare a 1.4 GHz P3 to a 1 GHz McKinley and see where >>>>this Crafty performance increase is coming from? I'm not at all familiar with >>>>McKinley, but would it be possible to run a version of Crafty compiled for >>>>32-bits on a McKinley and compare that to a Crafty compiled for 64-bits on >>>>McKinley? Is this a dumb idea? If this isn't possible, then it's going to be >>>>difficult to tell where the performance gain is really coming from. >>>> >>>>-Keith >>> >>>I don't know that you could do this. It would require that the compiler know >>>how to implement 64 bit ints as 2x32 bits, which on a mckinley would be a waste >>>of the compiler-writer's time... >> >>So what's wrong with Tom's suggestion - "You can make a bitboard class that >>contains two 32-bit ints and overload all the int operators and run it on a >>64-bit chip. ... renaming his source files from .c to .cpp and writing this >>simple class" >> >>Is this is a valid experiment then why not do it and settle the argument? >>Someone might even consider publishing a paper on it. (Maybe Tom would volunteer >>to hack the code if you don't want to bother?) If it's not valid then what's >>wrong with it? Do you think that the compiler would outsmart Tom and use 64-bit >>words for the bitboards anyways? >> >>What would your prediction for such an experiment be? That the version with 2 x >>32-bit bitboards would run half as fast as the version with 64-bit bitboards? >> >>I'm pretty sure that we could find some willing volunteers to run some simple >>experiments on their hardware. >> >>-Keith > > >It could certainly be done. However, I don't see what it would prove. >Other than that 64 bit operations are more efficient when done in one >"chunk" than in two. That seems intuitive anyway. It would also present >a few problems, with the FirstOne() and LastOne() PopCnt() functions that >use assembly on the PC but not on the 64 bit machines (yet). > >Remember that my comparison results are for the "best" 32 bit crafty I have >vs the 64 bit machines. Unfortunately, the 64 bit machines have no assembly >so they are at a significant disadvantage to start with, yet they are >blazingly fast. When I have access to one for a period of time, that >advantage will go away completely. Then it will be 32 vs 64 in a _real_ >comparison, not a biased-toward-32-bit mode as it is done today. I think the issue is that there may be other things (besides the word length) changed on the 64-bit processor which will also improve performance. I hope that at the very least you would also run other chess programs (non-bitboard) on the 64-bit processor and see what type of speed increase that they get versus older 32-bit processors. I think that the point of the experiment that we proposed "what it would prove" is what portion of the Crafty speed-up is due to the bitboard structures, and what portion is due to other factors. -Keith
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