Hello, I am attempting to get Open MPI to run over 2 nodes using a switch and a single breakout cable with this design:
(100GbE)QSFP <----> 2x (50GbE)QSFP Hardware Layout: Breakout cable module A connects to switch (100GbE) Breakout cable module B1 connects to node 1 RoCE NIC (50GbE) Breakout cable module B2 connects to node 2 RoCE NIC (50GbE) Switch is Mellanox SN 2700 100GbE RoCE switch * I am able to pass RDMA traffic between the nodes with perftest (ib_write_bw) when using the breakout cable as the IC from both nodes to the switch. * When attempting to run a job using the breakout cable as the IC Open MPI aborts with failure to initialize open fabrics device errors. * If I replace the breakout cable with 2 standard QSFP cables the Open MPI job will complete correctly. This is the command I use, it works unless I attempt a run with the breakout cable used as IC: mpirun --mca btl openib,self,sm --mca btl_openib_receive_queues P,65536,120,64,32 --mca btl_openib_cpc_include rdmacm -hostfile mpi-hosts-ce /usr/local/bin/IMB-MPI1 If anyone has any idea as to why using a breakout cable is causing my jobs to fail please let me know. Thank you, Brendan T. W. Myers brendan.my...@soft-forge.com <mailto:brendan.my...@soft-forge.com> Software Forge Inc
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