MutliPV behavior?

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Ovyron
Posts: 1948
Joined: Tue Jul 03, 2007 2:30 am

Re: MutliPV behavior?

Post by Ovyron » Wed Jan 31, 2018 12:13 am

Joerg Oster wrote:In SMP mode, I want to do a full PV search for all root moves,
eventually splitting the root moves over all helper threads.
What's the difference between this and setting MultiPV to the maximum?

syzygy
Posts: 4221
Joined: Tue Feb 28, 2012 10:56 pm

Re: MutliPV behavior?

Post by syzygy » Wed Jan 31, 2018 7:48 am

Ovyron wrote:
Joerg Oster wrote:In SMP mode, I want to do a full PV search for all root moves,
eventually splitting the root moves over all helper threads.
What's the difference between this and setting MultiPV to the maximum?
Setting MultiPV to the maximum performs a regular full search on all moves to find the best move, then a regular full search on all moves minus the best one to find the second best move, etc.

This is easy to implement, but seems suboptimal. Of course the transposition table helps to avoid double work.

Joerg Oster
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Joined: Fri Mar 10, 2006 3:29 pm
Location: Germany

Re: MutliPV behavior?

Post by Joerg Oster » Wed Jan 31, 2018 10:06 am

Ovyron wrote:
Joerg Oster wrote:In SMP mode, I want to do a full PV search for all root moves,
eventually splitting the root moves over all helper threads.
What's the difference between this and setting MultiPV to the maximum?
The difference is I don't switch the main search thread into MultiPV mode, but only the helper threads.

First tests indicate that I eventually need to modify the TT probing, too.
The helper threads already showed a mate score on a test position,
yet the main thread didn't change to that move ...
Jörg Oster

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Ovyron
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Re: MutliPV behavior?

Post by Ovyron » Wed Jan 31, 2018 2:26 pm

Joerg Oster wrote:
Ovyron wrote:Thanks Joerg!
You're welcome!
Thanks for bringing this up.
You're welcome too! :)

Did your patch make it to Stockfish 9?

Joerg Oster
Posts: 609
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Location: Germany

Re: MutliPV behavior?

Post by Joerg Oster » Wed Jan 31, 2018 6:17 pm

Ovyron wrote:
Joerg Oster wrote:
Ovyron wrote:Thanks Joerg!
You're welcome!
Thanks for bringing this up.
You're welcome too! :)

Did your patch make it to Stockfish 9?
No, as I didn't create a pull request for it.
But I just started a discussion thread on this in the forum to get some feedback.
Jörg Oster

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