Yield helped, but
not as effectively as one might have imagined.
Yes, that's the impression I get as well, the master process might be
yielding, but it doesn't appear to be a lot. Maybe I should do this
differently to avoid this CPU usage in master. All I really want is to
execute another process somewhere on a free node in my MPI universe,
wait for it to be done and go on. From my limited understanding of MPI,
MPI_Comm_spawn() and MPI_Barrier() seemed just like what I needed, but
as I said, maybe there are other ways to do this.