Hi Nicholas, Assuming ParaView is using the same behavior as upstream hydra * -np 8 should launch 8 processes, 4 on each node * -np 4 should launch 4 processes, 2 on each node * To launch 4 processes on one node, try -hosts compute0:4,compute1:4 -np 4 * The number 4 behind each host instructs hydra to assign the first 4 ranks to the host before moving on to another assignment, the default is 1. Hydra uses round-robin assignment policy Hope it helps, -- Hui ________________________________ From: Nicholas Yue via discuss <[email protected]> Sent: Friday, May 6, 2022 11:11 AM To: [email protected] <[email protected]> Cc: Nicholas Yue <[email protected]> Subject: [mpich-discuss] mpiexec : multi nodes and multi-cores questions Hi, I am using mpiexec from Paraview which from the `help` print out, indicates that it is derived from MPICH ``` Please see the intructions provided at http://wiki.mpich.org/mpich/index.php/Using_the_Hydra_Process_Manager for further details ``` so I thought I might ask some questions on this mailing list. I have set up a two node cluster, each compute node has 4 cores To fully utilise all the cores in both nodes, is this the correct way to launch pvserver ? ``` /shared/ParaView-5.10.1-osmesa-MPI-Linux-Python3.9-x86_64/bin/mpiexec -hosts compute0,compute1 -np 8 /shared/ParaView-5.10.1-osmesa-MPI-Linux-Python3.9-x86_64/bin/pvserver ``` If I change to `-np 4` would mpiexec use only compute0 or would it still run on both compute0 and compute1 but use only 2 cores of each node ? Cheers -- Nicholas Yue https://www.linkedin.com/in/nicholasyue/