Author: Matthew Hull
Date: 07:29:48 05/05/04
Go up one level in this thread
On May 05, 2004 at 10:25:23, Matthew Hull wrote: >On May 05, 2004 at 04:44:19, martin fierz wrote: > >>On May 04, 2004 at 21:06:30, Robert Hyatt wrote: >> >>>On May 04, 2004 at 18:21:07, martin fierz wrote: >>> >>>>On May 04, 2004 at 13:44:21, Robert Hyatt wrote: >>>> >>>>>On May 04, 2004 at 10:49:42, martin fierz wrote: >>>>> >>>>>>On May 04, 2004 at 07:32:01, Rolf Tueschen wrote: >>>>>> >>>>>>>On May 04, 2004 at 07:11:15, martin fierz wrote: >>>>>>> >>>>>>>>On May 03, 2004 at 22:50:58, Robert Hyatt wrote: >>>>>>>> >>>>>>>>>If you recall, I _have_ given some error estimates in the past. Remember the >>>>>>>>>wildly varying speedup numbers I showed you the first time this issue came up? >>>>>>>> >>>>>>>>i recall that you gave wildly varying speedup numbers, and an explanation for >>>>>>>>why this happens. i don't recall a real error estimate, but that can be either >>>>>>>>because >>>>>>>>-> you gave one and i didn't see it >>>>>>>>-> you gave one, i saw it and forgot >>>>>>>>-> you didn't give one at all >>>>>>>> >>>>>>>>so... what kind of numbers would you give if you were pressed? >>>>>>> >>>>>>> >>>>>>>Isn't it impolite to imply the third option if Bob JUST said that he did give >>>>>>>some? >>>>>> >>>>>>no - asking questions always has to be allowed among scientists. forbidding to >>>>>>ask questions is the hallmark of religious fanatics and fascists... but i >>>>>>digress :-) >>>>>>bob says he gave numbers, which he did. but IIRC, he never gave an error >>>>>>estimate. so i am allowed to ask for it, and it is not at all impolite to do so. >>>>>>what he did show is the speedup in about 30 different positions, which could >>>>>>vary wildly depending on the position. >>>>>> >>>>>>i don't know why you think you have to stand up and defend bob every time >>>>>>somebody says something about him you don't like. just leave that up to him. he >>>>>>can take it :-) >>>>>> >>>>>>cheers >>>>>> martin >>>>> >>>>> >>>>>I wasn't offended. I hope my answer was ok. >>>> >>>>i didn't think you'd be offended, and your answer was ok, but...why don't you >>>>take N (preferably N>>30...) positions and compute the standard deviation of >>>>your speedup numbers, and the standard deviation of the average speedup? you can >>>>still discuss the meaning of this, but at least you have an error margin you can >>>>attach to your speedup. i don't see anything wrong with that!? even if the >>>>probability distribution is obviously not a normal distribution, you can >>>>probably approximate it as such, and get an idea of it's width from these >>>>numbers. >>>> >>>>>This is not an easy question to deal with. >>>> >>>>>IE if you take the standard deviation of a set of random numbers between >>>>>0 and N what do you get? That is what the speedup numbers look like for some >>>>>positions. For others the speedup is a near-perfect constant value. Add some >>>>>perfect constants plus some randomly distributed values and exactly what does >>>>>the SD show? :) >>>> >>>>i don't quite understand your question. if you take enough positions, then you >>>>will get something sensible, i would think. if you doubt this, you can take e.g. >>>>10'000 sequential positions from crafty's ICC log, and bunch them together in >>>>groups of 1000, and compute average speedup + stdev-of-average-speedup for each >>>>of the bunches. i can't imagine that you get 10 wildly differing values, as your >>>>statement above suggests. >>>> >>>>cheers >>>> martin >>> >>> >>>It isn't so easy to get speedup. IE how would I take a position that took X >>>seconds with 2 or 4 cpus and compute the 1 cpu time? Think about it carefully >>>and you will see the problem. How to get the 1-cpu test case to have a properly >>>loaded hash table, killer move table, history table, etc, before starting the >>>search??? >> >>i don't understand this part at all. run the exact same test on a 1 CPU machine, >>and then on an N-CPU machine. >>the reason i don't understand this at all is that all the details you are >>talking about are irrelevant. i want to know what happens if i run the same test >>positions on a 1 CPU box or on a N CPU box. this is easy to answer, because it >>can be determined experimentally. whether or not there are philosophical issues >>as those you raise above can be discussed, but it doesn't stop you from getting >>your number... >> >> >>>The best bet is to take N positions where N is large. But then that is not the >>>same as what happens in real games where the positions are connected via info >>>passed from search to search in the hash table. >> >>not true if you use 1000 positions from crafty's ICC log file, where the exact >>same thing happens, because these are also positions from real games, connected >>to each other. > > >The only way I can see how your idea would work is if crafty played a series of >games searching to a fixed depth with a single processor. Then take the >positions from those games and set them up in the order they occurred and time >crafty's response to those positions to the same depth, but with 2 processors, >then do it all over again with 3 processors, etc. That way for each run, the >effects of cache relavency are not lost as would be the case in disconnected >test set positions. > >Then you might have an idea of an expected speedup in actual games, rather than >from disconnected test positions. > >That is a much more involved and time consuming test. I don't think he could >have afforded that kind of CPU time on a CRAY. Not to mention that you would need to time the opponents response exactly for each test run to get the effects of pondering on cache as well, I would assume. Thats an extra complication. > > >> >>>It is just a very hard question to answer. And change the positions and you can >>>change the answer significantly... >> >>perhaps, perhaps not. you didn't measure it, and so you can't say :-) >> >>cheers >> martin
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