The two files have a slightly different format and completely different meaning. The hostfile specifies how many slots are on a node. The rankfile specifies a rank and what node/slot it is to be mapped onto.
In order to use "mpirun --rankfile", I also need to specify hosts/hostlist. But that information is redundant with what I provide in the rankfile. So, from a user's point of view, this strikes me as broken. Yes? Should I file a ticket, or am I missing something here about this functionality?
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