Hideki Kato wrote:
No. Remember UCT is a sequential algorithm. Parallelizing UCT make
playouts ineffective. Increasing the number of threads and/or
communicating delay decreases the effectiveness of the playouts. With
my experiments on a symmetrical threads implementation on a four core
SMP system, winning rate against GNU Go decreases from 50.4+-1.1%
to 46.7+-1.1%, which corresponds to -25 ELO, where 1.1% are the
standard deviations [1].
This just shows that this SMP implementation has no *effective* speedup,
but probably a effective slowdown. And so a loss of ELO is expected.
I clearly stated what I meant by effective:
"How much faster you find the correct move. Not interesting is: how many
positions you search per second or how many playouts you do per second."
The fact that parallel UCT is not the same as serial UCT does not change
anything at all with the above definition. Either it finds good moves
faster, and hence is stronger, or it does not.
--
GCP
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