Hi All, I'm trying to accomplish binding each of a number of openmp threads to a unique physical core. my system has 2 hyper-threads per core, I want to bind only 1 openmp thread per physical core and skip hyper-thread "slots". My system has 10 cores (20 if you count hyper-threads). I want to run 2 mpi ranks each with 5 openmp threads, and I want the threads on rank 0 to bind to core: 0,1,2,3,4  and the threads on rank 1 to bind to core: 5,6,7,8,9. I've tried combinations of -bind-to and -map-by but I'm experiencing that the openmp threads are always doubled up , the hyperthread slots are being used. For example (a.out here prints the thread affinity): $ export OMP_PLACES=threads OMP_PROC_BIND=true OMP_DISPLAY_ENV=TRUE OMP_NUM_THREADS=5 $ mpiexec -np 2 -bind-to core:5 -map-by hwthread:10 ./a.out | sort -k 4 OPENMP DISPLAY ENVIRONMENT BEGIN   _OPENMP = '201511'   OMP_DYNAMIC = 'FALSE'   OMP_NESTED = 'FALSE'   OMP_NUM_THREADS = '5'   OMP_SCHEDULE = 'DYNAMIC'   OMP_PROC_BIND = 'TRUE'   OMP_PLACES = '{0},{10},{1},{11},{2},{12},{3},{13},{4},{14}'   OMP_STACKSIZE = '0'   OMP_WAIT_POLICY = 'PASSIVE'   OMP_THREAD_LIMIT = '4294967295'   OMP_MAX_ACTIVE_LEVELS = '2147483647'   OMP_CANCELLATION = 'FALSE'   OMP_DEFAULT_DEVICE = '0'   OMP_MAX_TASK_PRIORITY = '0'   OMP_DISPLAY_AFFINITY = 'FALSE'   OMP_AFFINITY_FORMAT = 'level %L thread %i affinity %A' OPENMP DISPLAY ENVIRONMENT END OPENMP DISPLAY ENVIRONMENT BEGIN   _OPENMP = '201511'   OMP_DYNAMIC = 'FALSE'   OMP_NESTED = 'FALSE'   OMP_NUM_THREADS = '5'   OMP_SCHEDULE = 'DYNAMIC'   OMP_PROC_BIND = 'TRUE'   OMP_PLACES = '{5},{15},{6},{16},{7},{17},{8},{18},{9},{19}'   OMP_STACKSIZE = '0'   OMP_WAIT_POLICY = 'PASSIVE'   OMP_THREAD_LIMIT = '4294967295'   OMP_MAX_ACTIVE_LEVELS = '2147483647'   OMP_CANCELLATION = 'FALSE'   OMP_DEFAULT_DEVICE = '0'   OMP_MAX_TASK_PRIORITY = '0'   OMP_DISPLAY_AFFINITY = 'FALSE'   OMP_AFFINITY_FORMAT = 'level %L thread %i affinity %A' OPENMP DISPLAY ENVIRONMENT END Hello from rank 0, thread 0, on smic.dhcp. (core affinity = 0) Hello from rank 0, thread 1, on smic.dhcp. (core affinity = 10) Hello from rank 0, thread 2, on smic.dhcp. (core affinity = 1) Hello from rank 0, thread 3, on smic.dhcp. (core affinity = 11) Hello from rank 0, thread 4, on smic.dhcp. (core affinity = 2) Hello from rank 1, thread 0, on smic.dhcp. (core affinity = 5) Hello from rank 1, thread 1, on smic.dhcp. (core affinity = 15) Hello from rank 1, thread 2, on smic.dhcp. (core affinity = 6) Hello from rank 1, thread 3, on smic.dhcp. (core affinity = 16) Hello from rank 1, thread 4, on smic.dhcp. (core affinity = 7) *How do I get mpich to skip the hyper-threads (i.e. cores with number greater than 9)?* Here's an example that did work: export OMP_PROC_BIND=true OMP_DISPLAY_ENV=TRUE OMP_NUM_THREADS=5 export OMP_PLACES="{0},{1},{2},{3},{4},{5},{6},{7},{8},{9}" mpiexec -np 2 -bind-to core:5 -map-by core:5 ./a.out libgomp: Number of places reduced from 10 to 5 because some places didn't contain any usable logical CPUs OPENMP DISPLAY ENVIRONMENT BEGIN   _OPENMP = '201511'   OMP_DYNAMIC = 'FALSE'   OMP_NESTED = 'FALSE'   OMP_NUM_THREADS = '5'   OMP_SCHEDULE = 'DYNAMIC'   OMP_PROC_BIND = 'TRUE'   OMP_PLACES = '{0},{1},{2},{3},{4} libgomp: '   OMP_STACKSIZE = '0'   OMP_WAIT_POLICY = 'PASSIVE'   OMP_THREAD_LIMIT = '4294967295'   OMP_MAX_ACTIVE_LEVELS = '2147483647'   OMP_CANCELLATION = 'FALSE'   OMP_DEFAULT_DEVICE = '0'   OMP_MAX_TASK_PRIORITY = '0'   OMP_DISPLAY_AFFINITY = 'FALSE'   OMP_AFFINITY_FORMAT = 'level %L thread %i affinity %A' OPENMP DISPLAY ENVIRONMENT END Number of places reduced from 10 to 5 because some places didn't contain any usable logical CPUs OPENMP DISPLAY ENVIRONMENT BEGIN   _OPENMP = '201511'   OMP_DYNAMIC = 'FALSE'   OMP_NESTED = 'FALSE'   OMP_NUM_THREADS = '5'   OMP_SCHEDULE = 'DYNAMIC'   OMP_PROC_BIND = 'TRUE'   OMP_PLACES = '{5},{6},{7},{8},{9}'   OMP_STACKSIZE = '0'   OMP_WAIT_POLICY = 'PASSIVE'   OMP_THREAD_LIMIT = '4294967295'   OMP_MAX_ACTIVE_LEVELS = '2147483647'   OMP_CANCELLATION = 'FALSE'   OMP_DEFAULT_DEVICE = '0'   OMP_MAX_TASK_PRIORITY = '0'   OMP_DISPLAY_AFFINITY = 'FALSE'   OMP_AFFINITY_FORMAT = 'level %L thread %i affinity %A' OPENMP DISPLAY ENVIRONMENT END Hello from rank 0, thread 1, on smic.dhcp. (core affinity = 1) Hello from rank 0, thread 2, on smic.dhcp. (core affinity = 2) Hello from rank 1, thread 0, on smic.dhcp. (core affinity = 5) Hello from rank 0, thread 3, on smic.dhcp. (core affinity = 3) Hello from rank 0, thread 0, on smic.dhcp. (core affinity = 0) Hello from rank 1, thread 4, on smic.dhcp. (core affinity = 9) Hello from rank 0, thread 4, on smic.dhcp. (core affinity = 4) Hello from rank 1, thread 3, on smic.dhcp. (core affinity = 8) Hello from rank 1, thread 1, on smic.dhcp. (core affinity = 6) Hello from rank 1, thread 2, on smic.dhcp. (core affinity = 7) That's exactly what I want! *Could I accomplish this without setting OMP_PLACES list explicitly? And in the process hopefully avoid the libgomp warning. Is there some combination of -bind-to, -map-to that would achieve this result?* Thanks!