Check out the new MPI-3 function MPI_Comm_split_type that is supported by MPICH-3. Best, Jeff ----- Original Message ----- From: "Tatiana V. Martsinkevich" <[email protected]> To: [email protected] Sent: Wednesday, July 3, 2013 10:39:55 AM Subject: [mpich-devel] find out what processes are on the same node Hello, I have a couple of questions: 1) is there a way to find out what other processes reside in the same node as my_rank from within MPICH? I found this function: MPIR_Comm_is_node_aware(comm_ptr) and if it's true I can get access (although not always?) to comm_ptr->node_comm. I wonder what are the situations when I won't be able to know what processes are on the same node ( i.e. comm_ptr->node_comm is null) and is there any other way to get the info then? 2) MPIR_Comm_is_node_aware() returns true if comm->hierarchy_kind == MPID_HIERARCHY_PARENT and apparently there are the following hierarchies: /* flat, parent, node, or node_roots */ Could someone please explain what are each of the hierarchy? regards, -- Tatiana V. Martsinkevich PhD student INRIA Saclay, University of Paris Sud XI -- Jeff Hammond Argonne Leadership Computing Facility University of Chicago Computation Institute [email protected] / (630) 252-5381 http://www.linkedin.com/in/jeffhammond https://wiki.alcf.anl.gov/parts/index.php/User:Jhammond ALCF docs: http://www.alcf.anl.gov/user-guides