On Sep 5, 2014, at 3:34 PM, Allin Cottrell <cottr...@wfu.edu> wrote:
> 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). If you are going to treat hyperthreads as independent processors, then you should probably set the --use-hwthreads-as-cpus flag so OMPI knows to treat it that way > > 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. Could you pass along the warning? It should only give you a warning if the #procs > #slots as you are then oversubscribed. You can turn that warning off by just add the oversubscribe flag to your mapping directive > > 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 > _______________________________________________ > users mailing list > us...@open-mpi.org > Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users > Link to this post: > http://www.open-mpi.org/community/lists/users/2014/09/25284.php
