I am running Ubuntu 18.04.3 with MPICH 3.3~a2-4 and GFortran 4:7.4.0-1ubuntu2.3 and GCC 4:7.4.0-1ubuntu2.3CC on dual AMD EPYC 7742 processors with hyper threading enabled. My codes are written in MPI and Fortran. The dual AMD processors have 128 cores and 256 threads. I want to optimize the runtime for 4 mpi jobs running concurrently with 64 threads each. Some timings are provided here: 1. One mpi job with mpiexec.hydra -n 64 myprog => 57.32s 2. One mpi job with mpiexec.hydra -bind-to numa -n 64 => 50.52s 3. Two mpi jobs with mpiexec.hydra -n 64 myprog => 99.77s 4. Two mpi jobs with mpiexec.hydra -bind-to numa -n 64 => 72.23s 5. Four mpi jobs with mpiexec.hydra -bind-to numa -n 64 => 159.2s The option "-bind-to numa" helps, but even so, running four mpi jobs concurrently with 64 threads each is considerably slower than running one mpi job with 64 threads. I can almost run four mpi jobs sequentially and match the time for running four mpi jobs concurrently. How can I improve on the result for running 4 mpi jobs concurrently? Thanks, Doug.