Le 14/02/2011 07:43, Siew Yin Chan a écrit :

No. Each hwloc-bind command in the mpirun above doesn't know that there are other hwloc-bind instances on the same machine. All of them bind their process to all cores in the first socket.

=> Agree. For socket:0.core:0-3 , hwloc will bind the MPI processes to all cores in the first socket. But how are the individual processes mapped on these cores? Will it be in this order:

rank 0 à core 0

rank 1 à core 1

rank 2 à core 2

rank 3 à core 3

Or in this *arbitrary* order:

rank 0 à core 1

rank 1 à core 3

rank 2 à core 0

rank 3 à core 2

The operating system decides where each process runs (according to the binding). It usually has no knowledge of MPI ranks. And I don't think it looks at the PID numbers during the scheduling. So it's very likely random.

Please distinguish your replies from the test you quote. Otherwise, it's hard to understand where's your reply. I hope I didn't miss anything.