Exact schedulability analysis of systems based on multi-rate periodic cyclic executives

In a recent survey of industry practitioners in the field of real-time systems, the majority of the respondents indicated that cyclic executives are (still) in use in their systems. Unfortunately, contemporary text books hardly address cyclic executives, if at all. There is therefore a need for analysis techniques for these executives. In this paper, we consider the multi-rate periodic cyclic executive, scheduling a given sequence of independent hard real-time polling tasks in a single-processor system. We present exact analysis for this cyclic executive, and discuss its relative strengths and weaknesses compared to multi-rate AFAP (as fast as possible) and multi-rate time-driven AFAP cyclic executives in terms of jitter, energy efficiency, schedulability, and implementation overhead. Unlike existing approaches, which typically take periodic tasks as a starting point for cyclic executives and focus on schedulability of tasks, we take the schedulability of the system as a starting point, i.e. whether or not the system meets its deadlines. In particular, we do not assume periods and deadlines for tasks, and our analysis derives feasible cycle times of a multi-rate periodic cyclic executive for a system.