In this paper we present an extension to current schedulability analysis techniques for periodic tasks with offsets, scheduled under a preemptive fixed priority scheduler. Previous techniques allowed only static offsets restricted to being smaller than the task periods. With the extension presented in this paper, we eliminate this restriction and we allow both static and dynamic offsets. The most significant application of this extension is in the analysis of multiprocessor and distributed systems. We show that we can achieve a significant increase of the maximum schedulable utilization by using the new technique, as opposed to using previously known worst-case analysis techniques for distributed systems. ___________________

Abstract1This paper considers the problem of fixed priority scheduling of periodic tasks where each task's execution priority may vary. Periodic tasks are decomposed into serially executed subtasks. where each subtask is characterized by an execution time and a fixed priority, and is permitted to have a deadline. A method for determining the schedulability of each task is presented along with its theoretical underpinnings. This method can be used to analyze the schedulability of complex task sets which involve interrupts, certain synchronization protocols, nonpreemptible sections and, in general, any mechanism that contributes to a complex priority structure. The method is illustrated with a realistic example.

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