Resource reclaiming in hard real-time systems with static and dynamic workloads

Abstract

The paper addresses resource reclaiming in the context of non-preemptive priority list scheduling for hard real-time systems. Such scheduling is inherently susceptible to multiprocessor timing anomalies. The authors present low overhead run-time stabilization methods for a general tasking model that allows phantom tasks as a mechanism to model processor external events. A family of scheduling algorithms is defined, that guarantees run-time stabilization for systems consisting of tasks with hard and soft deadlines. The later, i.e. soft tasks, may arrive dynamically. Stabilization is addressed in the context of dynamic and static task to processor allocation. Previous stabilization methods, focused on a priori stabilization for static workloads with dynamic task to processor allocation, thus cannot support this general scheduling model. By taking advantage of run-time information, the stabilization algorithms use the scan-window approach to prevent instability from occurring. Mechanisms are introduced that explicitly control the run-time behavior of tasks with hard deadlines. As a consequence, processor resources become available that can be used to improve processor utilization and response time of soft tasks. The resulting scan algorithms are intended for real world applications where low run-time overhead and a realistic task model are needed.