I am experimenting with MPI (world) across different systems. One system is a Xeon Phi KNL (64 cores, 256 logical processors) called KNL, and the other system is an E5-2620v2 (6 cores, 12 logical processors) called Thor.
What I intended to do is do is to partition the KNL into 2 ranks, and then run the 3rd rank on the E5-2620v2.
mpirun -n 3 -ppn 1 -hosts KNL,KNL,Thor program arg arg arg
This launches 2 ranks on KNL and 1 rank on Thor as expected
So far, so good.
Rank 0 was located on KNL
Rank 1 on Thor
Rank 2 on KNL
Aren't the nodes associated in the -hosts order?
What is the recommended way to control rank placement?
When I try 8 on KNL and 1 on Thor, the distribution is quite goofy. (likely my issue)
I tried using the : separator to sequester the KNL on left side and Thor on right side of :, but mpirun choked on the comman line.
(I am a noob at this)
Jim Dempsey