Author: Daniel Shawul
Date: 09:34:20 08/25/05
Go up one level in this thread
On August 24, 2005 at 23:22:50, Robert Hyatt wrote: >On August 24, 2005 at 22:23:11, James Swafford wrote: > >> >>I'm sure most parallel searchers use algorithms that allow splitting >>at arbitrary nodes in the tree. I'm curious how good (or bad!) >>it would be to simply spawn threads at the root to search an entire >>move. >> >>In other words, if I have 4 processors, then I would have 4 search >>threads running, each searching a different root move. > >Here's an assignment. Take your favorite program, and set up a middlegame >position. Let it start searching. When an iteration takes at least a minute, >pay careful attention, and watch your time when it starts the next iteration. >Watch carefully and notice when it pops up a score for the first move and goes >on to the next move. Then watch carefully until that iteration ends. > >Here is the question. > >You have three times. > >time(iteration start) >time(first score displayed) >time(iteration ended) > >look at the difference between the first two, and compare that to the difference >between the last two divided by #legal_moves-1... > >You will note that the first move takes _way_ more time than all the other moves >combined. now guess what happens when you search the second-best move first? >It takes as long as the first move. And then guess how long the first move >takes? Same time it took before. > >Bottom line is that this only gives you a very tiny speedup. Maybe 1.5X if you 1.5X ? i think that is too big. Last time i tried PVsplit , it only gave 1.2-1.3 speed up. If what you said is correct , i should probably try it. daniel >are lucky. We used this in the very first parallel search we did. Because we >had no time to develop something better for that ACM event. It was not good. > >Even worse, what about positions where you just have one or two legal moves? :) > > >> >> Yes, I know that's incredibly simplistic. I'm just curious as to >>how the naive approach compares to something more complex. > >Poorly. _very_ poorly. :) > > >> >>Thanks, >>-- >>James
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