Thanks. Why should we care of the node number? I think users care primarily of the maximum number of the MPI processes they can reasonably use without oversubscribing the system. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Josh Hursey Sent: Wednesday, February 17, 2010 2:17 PM To: MPI 3.0 Fault Tolerance and Dynamic Process Control working Group Subject: [Mpi3-ft] MPI_UNIVERSE_NUM_NODES? I have been talking with a couple application groups that are interested in using comm_spawn for dynamic resource management scenarios. MPI_UNIVERSE_SIZE (MPI 10.5.1) is a good starting place for them to portably find a soft limit on the number of processes that can be started within their allocation. However, they would also really like to know how many machines/nodes are in their allocation in an equally portable way (So they can try to create N procs per node, for example). Currently they do some preprocessing on the runtime environment variables to determine how many nodes are in the allocation. Since this is something the MPI implementation is already doing, I suggested that it might be possible to expose this in a portable way to the application through the MPI interface. So I am proposing a MPI_UNIVERSE_NUM_NODES attribute to MPI_COMM_WORLD with similar wording as MPI_UNIVERSE_SIZE. This will let the application access the number of nodes in their allocation in a portable manner. As for on-node topologies (i.e., sockets, cores, etc.), there are other tools to help make that more portable (e.g. hwloc). I am interested in what others think of the idea of introducing a MPI_UNIVERSE_NUM_NODES attribute to the standard. Cheers, Josh _______________________________________________ mpi3-ft mailing list [email protected] http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-ft --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies.