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Subject: Re: Non-deterministic behaviour - The Road to a Heaven of Genius?

Author: Dan Honeycutt

Date: 10:22:15 01/03/06

Go up one level in this thread


On January 02, 2006 at 07:29:01, Rolf Tueschen wrote:

>On January 01, 2006 at 14:36:08, George Sobala wrote:
>
>>On January 01, 2006 at 11:17:26, Robert Hyatt wrote:
>>
>>>On December 31, 2005 at 17:41:27, George Sobala wrote:
>>>
>>>>I was playing around with seeing how Deep Shredder performs with different
>>>>numbers of threads, and was fascinated to discover that the program behaviour
>>>>becomes completely non-repeatable / non-deterministic once more than one thread
>>>>is running.
>>>
>>>This is perfectly normal, and every parallel search program (that is any good)
>>>exhibits this same behavior.  It's just something one lives with to obtain the
>>>improved performance.
>>>
>>>
>>>>
>>>>With multiple threads, no analysis is the same two times running. The time to a
>>>>solution of a problem varies wildly from run to run. This may come as no
>>>>surprise to multi-processing experts amongst you but I was certainly surprised
>>>>by the magnitude of the differences in time-to-solve between different runs.
>>>
>>>We've had threads here in the past about this.  Some positions produce wildly
>>>varying speedups.  Some produce very consistent speedups.  The only thing
>>>consistent is that things are consistently inconsistent for the most part. :)
>>>
>>
>>Thanks, Robert. I thought I remembered something you had posted before about
>>this, but had mentally pegged the phenomenon as perhaps creating a 10-15%
>>variation. The unpredictable 20x speed I have seen astonished me: it is almost
>>like getting something for nothing - throw 4 threads at the task and there is a
>>chance you can get 20x performance. Or not. Depends on how the computer is
>>feeling today.
>>
>>These multithreaded engines would seem to display interesting characteristics:
>>
>>They won't play the same game twice, they can have flashes of genius ... or be
>>inexplicably thick and slow on a certain day.
>>
>>There is no point trying to benchmark them by running them a single time through
>>a test suite. The results of a second run could be very different.
>>
>>Am I correct in assuming that the behaviour of parallel search engines cannot be
>>emulated? With a single threaded engine, you can emulate its behaviour e.g. by
>>running an emulator program on a mainframe, a programmable calculator or with a
>>stadium full of abacus users, or any other Turing machine. Your emulation may be
>>very slow or very fast, but you will get the same answer in the end. It seems
>>that this is not true of a parallel search engine. It is not a single Turing
>>machine but a group of Turing machines the interactions between which are
>>governed by "random" external influences which can greatly influence the outcome
>>of the task.
>
>
>I'm unhappy with your choice of speech. Feeling well, genius, group of Turing
>machines, greatly influence the outcome - do you really expect that a computer
>scientist begins to judge your wordings? You are good enough into this to know
>well enough that your speculations of something genial just through the
>indeterministic aspects of parallel processors - are wrong! Or you oversee the
>always existing aspect of playing good moves by "chance", without conscience, or
>even for the wrong reasons. If you mean that by parallel processoring the
>hazardious come better into computerized chess, well even this is an insinuation
>the computerchess programmers couldnt be happy with because it meant that they
>dont have an ordinary solution got good chess moves. Also then you cant expect a
>decent answer from the experts here. The aspect of troll comes to mind, although
>I do never use it but here I think I gave a couple of reasons for that verdict.
>Excuse me for pointing out the obvious.

What, Rolf, you don't think a computer might play based on how it feels on a
given day?  It would seem you have not done a great deal of SMP programming.

Best
Dan H.



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