In the context offied-priority scheduling, feasibility of a task set with non-preemptive scheduling does not imply the feasibility with preemptive scheduling and vice versa. In this paper; we use the notion of preemption threshold, first introduced by Express Logic, Inc. in their ThreadX real-time operating system, to develop a scheduling model that subsumes both preemptive and non-preemptive fixed priori0 scheduling. Preemption threshold allows a task to only disable preemption of tasks up to a speciJied threshold priority. Tasks having priorities higher than the threshold are still allowed to preempt. With this new scheduling model, we show that schedulability is improved as compared to both preemptive and nonpreemptive scheduling models. We develop the equations f o r computing the worst-case response times, using the concept of level-i busy period. Some useful results about the generalized model are presented and an algorithm f o r optimal assignment of priori0 and preemption threshold is designed based on these results.
Preemption threshold scheduling REF is a dual priority scheduling technique.
Scheduling fixed-priority tasks with preemption threshold
Proceedings Sixth International Conference on Real-Time Computing Systems and Applications. RTCSA'99 (Cat. No.PR00306)
Proceedings Sixth International Conference on Real-Time Computing Systems and Applications. RTCSA'99 (Cat. No.PR00306)
Computer Science