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, jitters, 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 project we are developing a theory and practice of feedback control real-time scheduling. Feedback control real-time scheduling defines error terms for schedules, monitors the error, and continuously adjust the schedules to maintain required and stable performance. We have developed a practical feedback control real-time scheduling algorithm, FC-EDF, which is a starting point in the long-term endeavor of creating of theory and practice of feedback control scheduling. We are applying out results to applications such as web servers, agile manufacturing, and defense systems. We are also proposing a novel way to specify and measure complex real-time systems based on control theory.