Combining Static and Dynamic Scheduling for Real-Time Systems

We address in this paper the combination of static and dynamic scheduling into an approach called quasi-static scheduling, in the context of real-time systems composed of hard and soft tasks. For the particular problem discussed in this paper, a single static schedule is too pessimistic while a purely dynamic scheduling approach causes a very high on-line overhead. In the proposed quasi-static solution we compute at design-time a set of schedules, and leave for run-time only the selection of a particular schedule based on the actual execution times. We propose an exact algorithm as well as heuristics that tackle the time and memory complexity of the problem. The approach is evaluated through synthetic examples.