--hostfile option not working as expected

[rhl-bthr]

--hostfile option not working as expected

[rhc54]

Yes, that is exactly as it should do. I'd suggest reading the hostfile documentation - it explains all this and provides examples.

[rhl-bthr]

Sorry, maybe I should have been clearer. Running mpi with 2 hosts in the hostfile, and setting -np 2, still runs both processes on the same one host, and none on the other. My expectation was that it would run one process per host.

Is this behaviour expected? If so, is there a way I can use -hostfile but still enforce the behavior that runs one process per host, which is what I'm getting when I run mpi with the setting mpirun -host 10.4.0.1,10.4.0.2 -np 2 hostname

[rhc54]

Sorry, maybe I should have been clearer. Running mpi with 2 hosts in the hostfile, and setting -np 2, still runs both processes on the same one host, and none on the other. My expectation was that it would run one process per host.

No, that expectation is not correct. You really should read the hostfile doc - we spent quite a bit of time on it to ensure it clearly explained all this.

If so, is there a way I can use -hostfile but still enforce the behavior that runs one process per host, which is what I'm getting when I run mpi with the setting mpirun -host 10.4.0.1,10.4.0.2 -np 2 hostname

Sure - but the precise syntax depends on which OMPI version you are using (which you haven't told us). You might want to try mpirun --help or check the mpirun documentation for placement options.

[rhl-bthr]

Ah thanks, found it.

In case someone runs into this issue, I was able to solve this issue in two ways - by either adding -N 1 or --map-by-ppr:1:node. I was using OMPI version 4.0.3