Non-preemptive Fixed Priority Scheduling of Hard Real-Time Periodic Tasks

This paper addresses the problem of scheduling periodic tasks on a uniprocessor using static priority assignment without preemption. The problem of non-preemptive fixed priority scheduling has received little attention until recently, while real-life applications are often based on non-preemptive systems especially in case of embedded systems. In this paper, we show that Rate Monotonic priority assignment is optimal for non-preemptive scheduling when each task's relative deadline is equal to its period. We have derived a schedulability bound for non-preemptive Rate Monotonic scheduling by using period ratio of the tasks to provide a guarantee that tasks will meet their deadlines. Since the obtained bound is relatively small comparing with the preemptive scheduling, we also propose a method for designing high-utilization non-preemptive system to enhance the utilization bound.