Integration of Preemption Threshold and Quantum-Based Scheduling for Schedulability Enhancement of Fixed Priority Tasks

Fixed priority scheduling is an important real-time scheduling scheme widely used in practice. To improve the schedulability of fixed priority scheduling considerable effort has been made such as introduction of preemption threshold or deferred preemption, and quantum-based scheduling. In this paper, we develop a new scheduling scheme by introducing both preemption threshold and quantum into one scheduling framework. The new scheduling method may successfully schedule tasks which are not schedulable either by preemption threshold scheduling or quantum-based scheduling, as well as tasks schedulable by either scheduling, thus improves the schedulability of fixed-priority tasks. We analyze the schedulability of the new scheduler by computing the worst case response time of tasks. Based on the analysis, we developed an algorithm for assignment of preemption threshold and quantum sizes.