I suspect there is a new (to openmpi 1.8.N?) warning with respect to
requesting a number of MPI processes greater than the number of
"real" cores on a given machine. I can provide a good deal more
information is that's required, but can I just pose it as a question
for now? Does anyone know of a a relevant change in the code?
The reason I'm asking is that I've been experimenting, on a couple
of machines and with more than one computational problem, to see if
I'm better off restricting the number of MPI processes to the number
of "real" or "physical" cores available, or if it's better to allow
a larger number of processes up to the number of hyperthreads
available (which is twice the number of cores on the machines I'm
working on).
It seems to me that openmpi >= 1.8 is giving me a (somewhat obscure
and non-user friendly) warning whenever I specify to mpiexec a
number of processes > the number of "real" cores -- even if the
computation is in fact completed faster that way -- and I'd like to
track down what has changed.
As I indicated, I'll be happy to provide more information if this is
not enough to understand what I'm talking about.
--
Allin Cottrell
Department of Economics
Wake Forest University
