Author: Roberto Waldteufel
Date: 15:35:05 06/25/98
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On June 25, 1998 at 14:02:02, Robert Hyatt wrote: >On June 25, 1998 at 13:56:05, Robert Hyatt wrote: > >>On June 25, 1998 at 13:46:06, Roberto Waldteufel wrote: >> >>> >>>On June 25, 1998 at 12:03:11, Robert Hyatt wrote: >>> >>>>On June 25, 1998 at 04:54:02, Roberto Waldteufel wrote: >>>> >>>>> >>>>>Here's another question about Hsu's chess chip. I seem to recall reading some >>>>>time ago that Hsu was considering a commercial release of his chip. Does anyone >>>>>know anything more about this? If the chip were to become available, how could I >>>>>use it in conjunction with a PC? would the fixed depth not be "out of sync" for >>>>>the speed of, eg a Pentium 333Mhz if it was designed to work with a >>>>>supercomputer, or can the fixed depth be adjusted to redo the balancing act in >>>>>the new environment? If it were possible, I would be very interested in >>>>>experimenting with this sort of hardware coupling. I assume that it would extend >>>>>the depth to which a program could search by something like 4 extra plies within >>>>>the same time. This would surely improve the strength of the PC ches programs >>>>>quite a lot! >>>>> >>>>>Roberto >>>> >>>>there really isn't a "fixed depth". This is a parameter you set in the chess >>>>processor when you fire it up. You simply tell it to search to a depth of your >>>>choosing, although this depth has to be closely matched to the speed of the host >>>>machine as I mentioned in the past. Since the chess processor has a fixed clock >>>>speed of 2.4M nodes per second, you have to choose how deep it searches to >>>>balance that speed against the host machine that has to provide it positions to >>>>search. Set the depth too high and the host will waste time waiting on the >>>>chess processor. Set the depth too low, and the host will have to search an >>>>extra ply deeper to be able to provide the chess hardware positions quickly >>>>enough to keep it busy. >>>> >>>>If you study this, what you find is an interesting phenomonon. If you tell the >>>>chess processor to search 1 ply deeper, then the host processor has to search >>>>one ply shallower, or it will provide positions faster than the chess processor >>>>can search them and return the results. If you tell the chess processor to >>>>search one ply shallower, then the host processor has to search one ply deeper >>>>to provide it positions to search fast enough. In short, for a given host, >>>>there is a very definite max depth you can search. You can do more in the >>>>hardware, or more in the software. Software is generally better as you can >>>>change the search, tweak with the extensions, without changing the chess >>>>processors at all... >>>> >>>>Hope that explains what they are doing... >>> >>>Thanks for the info. I wonder if the theoretical limit problem could be overcome >>>in the same way that they did with Deeper Blue, ie many chess processors in >>>parallel, or would this not be practical for a pentium host? >>> >>>Best wishes, >>> >>>Roberto >> >>if life were only so simple. :) >> >>the point is, for any specific host machine, there is an optimal number of >>chess processors for a host machine. If you get too many chess processors, >>the host can't keep them busy unless you increase the depth on each chess >>processor by a ply so that the search on the hardware takes longer. But if >>you do this, the host can't keep up unless you reduce the depth by 1 ply, so >>you gain *nothing*. >> >>There is a constant ratio between the host processor and the number of chess >>processors. To go faster, you can double both, or to get cheaper you can divide >>both by 2, but you can't vary the number of chess processors without varying the >>number of host processors, *or* (perhaps) getting a single host processor that >>is twice as fast, which would let you keep 2x the chess processors busy. >> >>that's why they used a Scalable SP machine... if they want to double the number >>of chess processors (to double their NPS) they have to double the host as well. >> >>Bob > > >just thought of another way to explain this: > >think of the complete tree laid on it's side as a graph, with the root position >on the left, and tip positions to the right. You have two pieces of hardware, >the host and the chess processor. The chess processor is going to search the >positions on the right side of this graph, and the host is going to search the >positions on the left side. Draw a line vertically to separate the tree into >the left-half and right-half. Where do you draw this line so that what is to >the left is searched on the host, and what is on the right is searched on the >chess procssor? > >if you draw it too far to the right, the host does more work and gives the chess >processors tiny little trees to search. If you move it to the left, the host >searches a pretty small tree, but the work done by the chess processor is going >to be proportionally larger, because all that stuff has to be searched to reach >the same depth. > >So, in such a case, the host is waiting on the chess processor, while in the >first case, chess processors are waiting on the host. Ideal condition is to >have *both* host *and* chess processor busy 100% of the time. That occurs when >you get that vertical line in just the right place, so that the host can just >barely keep up with supplying the chess processor with positions, and the chess >processor is just barely keeping up with the positions the host is sending it. > >There you get maximal performance. Move the line left or right, and one will >start waiting on the other. With a loss of performance... > >Maybe that makes more sense that way? > >Bob Hi Bob, Thanks, I understand fine now. Even so, if the ratio is fairly close to the optimum, the overall effect compared to host alone would surely be a huge speedup, don't you think? I'm just hungry (even greedy!) for the most speed I can get. I think that no matter how deep I manage to search, I will always have an eye open for some way achieve that elusive extra ply. Perhaps the Alpha chip is a more practical (ie available) way to upgrade my hardware from Pentium, but I would imagine a chess processor (or several) would be the most dramatic of improvements. Best Wishes, Roberto
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