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Subject: Re: The need to unmake move

Author: Robert Hyatt

Date: 08:10:36 09/04/03

Go up one level in this thread


On September 04, 2003 at 04:54:53, Tony Werten wrote:

>On September 03, 2003 at 10:44:11, Sune Fischer wrote:
>
>>On September 03, 2003 at 10:35:11, Gian-Carlo Pascutto wrote:
>>
>>>On September 03, 2003 at 10:26:19, Sune Fischer wrote:
>>>
>>>>>What is your point?
>>>>
>>>>Heh :)
>>>>
>>>>You said (remote) checking for fail_high conditions at every node was required,
>>>>and I disagree.
>>>
>>>I never say 'at every node'.
>>
>>You said constantly, then I don't know what you mean by that.
>>
>>>Each time you get a subtree score, you must send out the score update to
>>>all processors, or store it locally and rely on remote processors to check
>>>it in your memory.
>>>
>>>Either way, you need remote accesses.
>>>
>>>Got it now?
>>
>>This is an entirely different matter, you don't get subtree scores "constantly".
>>
>>And I still say you only have to access when there is something to communicate.
>>
>>If you just quietly exit the subtree on a fail low, I see no need for
>>communication.
>
>I suddenly see the point you're missing. What you describe works correct on a
>dual machine only.
>
>Think about a 4 processor machine.
>
>processor 1 and 2 are running.
>
>processor 3 runs and starts a new thread on proc. 4
>
>Now proc 4 is done, proc 3 get's this (ie he get's a done message, with score )
>
>But how are proc 1 and 2 going to know that 4 is available ?
>
>Tony

Lock();
idle++;
Unlock();

and that does it.  _everybody_ can see "idle" (which is zero 99.9999% of the
time since processors are not idle that often).  The value is in local cache,
it costs nothing to test frequently, until a cache snoop discovers the valueeeee
has been changed.

The lock can be eliminated if desired, by using a somewhat different meaning for
"idle".

>
>>
>>-S.
>>>--
>>>GCP



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