$ cat hosts_file
knl-lb0:1
mic0:2
mic1:2

$ mpirun -machinefile hosts_file -n 5 ~/mpitest
Hello world: rank 0 of 5 running on knl-lb0
Hello world: rank 1 of 5 running on mic0
Hello world: rank 2 of 5 running on mic0
Hello world: rank 3 of 5 running on mic1
Hello world: rank 4 of 5 running on mic1
FROM RANK 0 - numthreads = 64
FROM RANK 1 - numthreads = 136
FROM RANK 3 - numthreads = 136
FROM RANK 2 - numthreads = 136
FROM RANK 4 - numthreads = 136
Elapsed time from rank 0:   11260.03 (usec)
Elapsed time from rank 1:   71480.04 (usec)
Elapsed time from rank 2:   69352.15 (usec)
Elapsed time from rank 3:   74187.99 (usec)
Elapsed time from rank 4:   67718.98 (usec)
rank 0 pi=   3.141598224640