From what I can tell, the info keyvals are not being sent to the process manager, which would explain what you are seeing. Need to investigate why that is happening next. What is your MPICH ./configure line? That'll help narrow where to look. Ken On 1/28/22, 12:49 PM, "Mccall, Kurt E. (MSFC-EV41)" <[email protected]> wrote: Ken, There is a lot of my own output mixed up in the "mpiexec -v" output. I hope you can make sense of this. Thanks, Kurt -----Original Message----- From: Raffenetti, Ken <[email protected]> Sent: Friday, January 28, 2022 12:36 PM To: Mccall, Kurt E. (MSFC-EV41) <[email protected]>; [email protected] Subject: [EXTERNAL] Re: [mpich-discuss] MPI_Comm_spawn crosses node boundaries "ip_address" won't be recognized, only "host", "hosts", or "hostfile". Could you run an example using "mpiexec -v" and capture/share the output? That should help tell us if the hostname information is being fed correctly to the process manager by the spawn command. Ken On 1/28/22, 11:35 AM, "Mccall, Kurt E. (MSFC-EV41)" <[email protected]> wrote: Ken, I'm using sbatch, which calls a bash script that calls mpiexec (4.0rc3). Which host name convention is correct, the short or the long host name? Would the "ip_address" info key work? Kurt -----Original Message----- From: Raffenetti, Ken <[email protected]> Sent: Friday, January 28, 2022 10:49 AM To: [email protected] Cc: Mccall, Kurt E. (MSFC-EV41) <[email protected]> Subject: [EXTERNAL] Re: [mpich-discuss] MPI_Comm_spawn crosses node boundaries Are you using mpiexec or srun when initially launching your job? Hydra (mpiexec) should support the "host" info key, but I'm not sure if srun will. Ken On 1/28/22, 10:41 AM, "Mccall, Kurt E. (MSFC-EV41) via discuss" <[email protected]> wrote: Hi, Running MPICH under Slurm, MPI_Comm_spawn unexpectedly creates new processes on any and all of the nodes that Slurm allocates to the job. I would like it to only create new processes locally on the node that called MPI_Comm_spawn. I’ve tried passing MPI_Comm_spawn an info struct created like this: MPI_Info info; MPI_Info_create(&info); MPI_Info_set(info, "host", host_name); MPI_Info_set(info, "bind_to", "core"); where hostname = “n001” or even the full name “n001.cluster.pssclabs.com” but that doesn’t prevent the problem. Any suggestions? Thanks, Kurt