On the Efficient Scheduling of Non-Periodic Tasks in Hard Real-Time Systems -- Short Version

This paper presents linear time, on-line 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 $\Theta(n)$, 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 pseudo-polynomial time to guarantee on-line 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 $\Theta(n)$ and $\Theta(n+k)$, respectively, where $k$ is the number of pending firm tasks.