Design and evaluation of a feedback control EDF scheduling algorithm

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 feedback control real-time scheduling algorithm and its evaluation. Performance results demonstrate the effectiveness of the algorithm when execution times vary from the worst case and when there are major shifts of total load in the system. A key part of this feedback solution is its explicit use of deadline based metrics.