On any PV-WAVE platform supporting OpenMP, it is possible to set the number of threads to a value that exceeds the number of available processors on your machine. This situation is known as 'over-subscription' and degrades performance. It is also possible to create this situation without explicitly setting the number of threads to a bad value. For example, if you simultaneously call PV-WAVE from multiple threads of an external C or FORTRAN application, PV-WAVE would then attempt to create its full complement of threads—leading to over-subscription. It is recommended that you call PV-WAVE from a single thread and allow PV‑WAVE to use all of the threads it needs.