It looks like we have a clear trend now. Light play-outs do not scale
as well as heavy play-outs.
I don't know if the data are sufficient for this conclusion, but another
element is that heavy playouts are seemingly easier to parallelize than
light playouts. This is tested clearly in multi-core parallelization, but
I guess it should also hold for mpi-parallelization (I've not sufficiently
tested to be very sure of that).
By the way, for 19x19, I have not yet found bounds on the increase
of efficiency of mogo as we increase the number of nodes. If someone
has a huge cluster with good nodes and a good switch, I would be very
happy to have a try on mogo on, say 10 000 cores, if someone has something
like that.
The current code
almost sacrifices one core for MPI, but we can improve that for
clusters with small numbers of cores per node. With 64 4-core nodes,
we have 95% winning rate against one node. I guess it is better with
more cores as one core is lost for MPI (on N cores, we loose nearly 1/N
for the MPI parallelization).
Perhaps MoGo stops improving beyond 64 nodes, but perhaps not :-)
Olivier
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