Real-time uniprocessor scheduling with fewer preemptions

In this paper, we propose a simple, but effective scheduling framework for EDF and RM, which reduces the number of preemptions by simply introducing a dummy task. We first observe useful preemption behavior under EDF and RM, leading to an interesting finding: an effective way to reduce the number of preemptions is to prevent jobs of a task with the smallest task period from preempting other jobs upon their release. To achieve this, we add a dummy task that invokes its job only when a newly-released job of the task with the smallest task period has a higher priority than the currently-executing job. Then, the currently-executing job can continue its execution without getting preempted by inheriting the priority of the dummy job. Since adding the dummy task can make a schedulable task set unschedulable, we propose how to set the dummy task’s parameters without compromising schedulability. In addition to the negligible overhead of this framework due to its simplicity, it holds an important property that does not increase the number of preemptions of any task set, compared to the original scheduling algorithm, which has not been achieved by existing studies. We also demonstrate via simulation that the proposed framework effectively reduces the number of preemptions under EDF and RM.