Author: Matthew Hull
Date: 09:12:59 05/05/04
Go up one level in this thread
On May 05, 2004 at 11:37:50, Robert Hyatt wrote: >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. >> >> > > >That is actually what I did. I used a Cray for about a year. Multi-cpu tests >could get about 5 minutes of "dedicated whole-machine" every hour followed by a >checkpoint and 55 minute wait for the next "slot". > >That's why I said it took way over a year to run all the tests to get the >results. Only exception was the 1 cpu tests which ran for long times, but with >1 cpu I could rely on CPU time rather than elapsed time. Even so, we still can't see the effect of pondering on the hash tables, since we are searching to a fixed depth. So the resemblance to real game conditions is still somewhat wanting. I have a tangential question. Assuming you have scads of memory, could you make a copy of the hash table(s) and ponder using the copy, then if the predicted move was not made, simply "context switch" to the before-ponder hash table? Would there be any benefit in that? Would such a copy operation not do for short time controls? > > > > > >>> >>>>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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