The case for feedback control real-time scheduling

Despite the significant body of results in real-time scheduling, many real world problems are not easily supported. While algorithms such as Earliest Deadline First, Rate Monotonic, and the Spring scheduling algorithm can support sophisticated task set characteristics (such as deadlines, precedence constraints, shared resources, jitter, etc.), they are all "open loop" scheduling algorithms. Open loop refers to the fact that once schedules are created they are not "adjusted" based on continuous feedback. While open-loop scheduling algorithms can perform well in static or dynamic systems in which the workloads can be accurately modeled, they can perform poorly in unpredictable dynamic systems. In this paper, we present a new scheduling paradigm, which we call feedback control real-time scheduling. Feedback control real-time scheduling defines error terms for schedules, monitors the error, and continuously adjusts the schedules to maintain stable performance. This paper also presents a practical feedback control real-time scheduling algorithm, FC-EDF, which is a starting point in the long-term endeavor of creating a theory and practice of feedback control scheduling.