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Subject: Re: Preparations for parallel search

Author: Robert Hyatt

Date: 07:08:20 07/09/04

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On July 09, 2004 at 09:53:02, Daniel Clausen wrote:

>On July 09, 2004 at 09:47:36, Tord Romstad wrote:
>
>>On July 09, 2004 at 09:13:31, Robert Hyatt wrote:
>>
>>>On July 09, 2004 at 08:38:31, Tord Romstad wrote:
>>>
>>>>I am currently writing a chess engine.  Parallel search is not among my main
>>>>interests at the moment, but it is not entirely impossible that I will give it
>>>>a try some time in the future.
>>>>
>>>>In order to keep everything as flexible as possible, I would like to design
>>>>my algorithms and data structures in such a way that adding parallel search
>>>>at a later stage is feasible.  I understand that I should remove most of my
>>>>global variables and replace them with huge structs containing the same data,
>>>>and use one such struct for each thread.  Is there anything else which is
>>>>important to keep in mind?
>>>>
>>>>Tord
>>>
>>>
>>>That's the main issue assuming you are going to use lightweight processes
>>>(threads) which I believe is the best approach.
>>
>>Yes, threads is what I intend to use.
>>
>>>The most thread-specific data
>>>you have, which means less global data, will help performance (modified global
>>>data is not cache-friendly on a SMP box) and simplify testing (since modified
>>>global data requires atomic locks to avoid interleaved update problems).
>>
>>But as far as I can see, I would be forced to pass an extra pointer to most
>>of the chess-related functions (search(), evaluate(), generate_moves(),
>>make_move() etc.).  A bit ugly, but I suppose I could live with that.
>
>What do you mean with ugly here?
>
>To me, functions which work on exactly the arguments they get and maybe return
>something are much clearer than functions which work on data that is cluttered
>all over the place. :)
>
>Sargon

A pointer requires a register.  The X86 doesn't have very many.  This turns into
an efficiency issue, but the gains far outweigh the small cost.




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