On the efficient scheduling of non-periodic tasks in hard real-time systems

The paper presents linear time, online algorithms which guarantee and jointly schedule firm aperiodic, hard sporadic and periodic tasks in fixed priority real time systems. We develop and capitalize on a methodology which computes the spare capacity Z(a,b) exactly in time Θ(n), for arbitrary schedule intervals (a,b), which, to the best of our knowledge, is the first linear time algorithm reported in the literature. Previous state of the art methods incur pseudopolynomial time to guarantee online a single aperiodic and incur continuous overhead for slack maintenance. Our method guarantees and schedules firm tasks to receive FIFO or EDF service, incurring a one-time linear cost of Θ(n) and Θ(n+k) respectively, where k is the number of pending firm tasks