Hi all, I just noticed a very strange behavior of the mpirun on KNL nodes. If I run 1 node with 1 MPI and 128 threads, everything goes well. If I run 2 nodes with 1 MPI and 128 threads on each nodes, all the 128 threads are actually running on a single core. This behavior is confirmed with KMP_AFFINITY=verbose. An extra question, is the currect mpirun aware of the omni path? I'm using the intel mpi comes with the compiler. Ye =================== Ye Luo, Ph.D. Leadership Computing Facility Argonne National Laboratory