Pre-scheduling: Integrating offline and online scheduling techniques

The issue of integrating event-driven workload into existing static schedules has been addressed by Fohler's Slot Shifting method [5] [6]. Slot Shifting takes a static schedule for a time-driven workload as input, analyzes its slacks off-line, and makes use of the slacks to accommodate an event-driven workload on-line. The Slot Shifting method does not address how to produce a static schedule which it assumes as given. We propose an integrated approach with an off-line pre-scheduler and an on-line scheduler. The pre-scheduler produces a pre-schedule of the time-driven workload with sufficient embedded slacks to accommodate the event-driven workload. The on-line scheduler schedules all workloads by EDF with one extra constraint: the order of execution of the time-driven workload must follow the pre-schedule. Our pre-scheduler produces a valid pre-schedule if and only if one exists and is therefore optimal. We shall show that the choice of the pre-schedule cannot be considered independent of the event-driven workload.