Reconciling Real-Time and Fair Scheduling

Multiprogramming operating systems which support both real-time and non-rea l-time processes are called soft-real-time systems. In such systems, process scheduling is problematic, because there are two qualitatively different classes of processes requiring scheduling. If the scheduling algorithm is designed to favor one class of processes, it will probably not treat the other class of processes fairly. For instance, priority-based schedulers are considered fair to non-real-time processes, but lead deadline-based schedules suffice to run real-time processes but will starve non-real-time processes, which have no deadline. The common conception is that real-time responsiveness and fair multiprogramming are mutually exclusive. The author holds that this concept is wrong, because our concept of fairness is wrong. He proposes a unifying model of processes under which so-called real-time and non-real-time processes are merely different instances of the same sort of object, with different attribute values. Under this unifying scheme, all processes can be treated fairly while still preserving real-time responsiveness.