Feasibility Analysis under Fixed Priority Scheduling with Fixed Preemption Points

Limited preemption models have been proposed as a viable alternative between the two extreme cases of fully preemptive and non-preemptive scheduling. In particular, allowing preemption to occur only at predefined preemption points reduces context switch costs, simplifies the access to shared resources, and allows more predictable estimations of worst-case execution times. Current results related to such a model, however, exhibit two major deficiencies: (i) The exact response time analysis has a high computational complexity; (ii) The maximum lengths of then on-preemptive regions was not completely investigated in all possible scenarios. In this paper, we address the problem of scheduling a set of real-time tasks having fixed priorities and fixed preemption points. In particular, under specific but not restrictive assumptions we simplified the feasibility analysis and proposed an efficient feasibility test. Finally, an algorithm for computing the maximum length of fixed non-preemptive regions for each task is described, and some simulation experiments are presented to validate the proposed approach.