Tie-breaking for EDF on multiprocessor platforms

Scheduling real-time systems on multiprocessors introduces complexities that do not arise when using uniprocessors. When scheduling using EDF on multiprocessor platforms, breaking deadline ties in different ways can change the resulting schedule dramatically. We consider methods to resolve the ambiguities in EDF priorities due to coincident deadlines. We show that no optimal ambiguity solver can be online. We also show that no optimal static tiebreaker exists even if we relax the on-line property.