Scheduling Fixed-Priority Tasks with Preemption Threshold An Attractive Technology?

While it is widely believed that preemptibility is a necessary requirement for developing real-time software, there are additional costs involved with preemptive scheduling, as compared to non-preemptive scheduling. Furthermore, in the context of fixed-priority scheduling, feasibility of a task set with nonpreemptive scheduling does not imply feasibility with preemptive scheduling (and vice-versa). In an earlier paper, we had developed the model of scheduling fixed priority tasks with preemption threshold, which unifies the concepts of preemptive and non-preemptive scheduling, and subsumes both as special cases. In this paper we provide evidence that this new scheduling model provides substantial quantitative benefits over both preemptive and non-preemptive scheduling models. We show that the new model can result in substantial improvement of schedulability by taking advantage of aspects of both preemptive and non-preemptive scheduling. Furthermore, we show that the new model provides lower run-time costs (in CPU overheads due to preemptions, and stack space for tasks) as compared to preemptive scheduling, even when a task set is schedulable under the preemptive scheduling model. We believe that the new scheduling model provides a compelling technology alternative, by providing high levels of schedulable utilization at lower costs.