On the characterization of the space of feasible WCETs for Earliest Deadline First scheduling

This paper presents a sensitivity analysis for the dimensioning of realtime systems in which sporadic tasks are executed according to the preemptive Earliest Deadline First (EDF) scheduling policy. The timeliness constraints of the tasks are expressed in terms of late termination deadlines. New results for EDF are shown, which enable us to determine the C-space feasibility domain valid for any configuration of Worst-Case Execution Times (WCETs), such that any task set with its WCETs in the C-space domain is feasible with EDF. We show that the C-space domain is convex, a property that can be used to reduce the number of inequalities characterizing the C-space domain. We propose another approach to reduce the number of inequalities based on the concept of worst-case busy period for WCETs in the C-space. We apply the two approaches on an example, and we compare the C-space obtained with EDF scheduling to the C-space obtained with Deadline Monotonic scheduling.