Preemptive Priority Based Scheduling: An Appropriate Engineering Approach

Scheduling theories for fixed priority scheduling are now sufficiently mature that a genuine engineering approach to the construction of hard real-time systems is possible. In this paper we review recent advances. A flexible computational model is adopted that can accommodate periodic and sporadic activities, different levels of criticality, process interaction and blocking, cooperative scheduling (deferred preemption), release jitter, precedence constrained processes, arbitrary deadlines, deadlines associated with specific events (rather than the end of a task's execution) and offsets. Scheduling tests for these different application characteristics are described. This model can be supported by structured, object oriented or formal development methods. The paper also considers the issues involved in producing safe and predictable kernels to support this computational model