Characterization of the Space of Feasible Worst-Case Execution Times for Earliest-Deadline-First Scheduling

Abstract

Thispaperpresentsasensitivityanalysisforthedimensioningofreal-timesystemsinwhich sporadic tasks are executed according to the preemptive earliest deadline first scheduling policy. The timeliness constraints of the tasks are expressed in terms of late termination deadlines. New results for earliest deadline first are shown, which enable us to determine the space of feasible worst-case execution times, denoted the C-space, valid for any configuration of worst-case execution times. The C-space is such that any task set with its worst-case execution times in the C-space domain is feasible with earliest deadline first. We show in a first approach 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 in another approach toreducethenumberofinequalitiesbasedontheconceptofworst-casebusyperiodforworstcase execution times in the C-space. This approach can be used for busy periods meeting a given property. We apply the two approaches on an example, and we compare the Cspace obtained with earliest deadline first scheduling to the C-space obtained with deadline monotonic scheduling.