Optimal Priority Assignment for Synchronous Harmonic Tasks with Dynamic Self-Suspension

Self-suspension behavior happens when a job has to wait for some activity to complete and results in substantial schedulability degradation in real-time systems. Despite extensive studies for self-suspending real-time task systems, the state of the art has barely addressed the optimality of the scheduling algorithms, especially for tasks with dynamic self-suspension. In this paper, we explore optimal priority assignment for periodic real-time tasks with dynamic self-suspension under Task-level Fixed-Priority (T-FP) scheduling. To that end, we provide exact schedulability tests for frame-based and synchronous harmonic tasks. We show that the Suspension-Aware Deadline-Monotonic (SADM) priority assignment is an optimal fixed-priority scheduler for many scenarios. Further, for cases where SADM is not optimal, we adopt Audsley's Optimal Priority Assignment (OPA) approach to derive an optimal fixedpriority assignment. Evaluation results show that the exact tests outperform state-of-the-art schedulability tests from the literature, and that optimal priority assignments significantly improve schedulability over classical priority assignments.