Comment (by Roland Haas):

might be better to add the hwloc libs etc to MPI_LIBS in the MPI thorn so that all MPI clients benefit from them (not just PETSc). Do you have any idea why only PETSSc seems to be affected by this (and no eg hdf5)?

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2969/externallibraries-petsc-link-hwloc-into