Quantum-Based Fixed Priority Scheduling

Fixed priority schedulers are widely used for real-time systems, and there were efforts to improve the schedulability. For example, preemption threshold scheduling increases the schedulability by introducing non-preemptiveness during task execution. In this paper, we study another scheduling model that can improve the schedulability of tasks: quantum-based scheduling. When quantum-based scheduling is combined with priority-based scheduling, the quantum introduces a partially non-preemptive region which causes a priority inversion. We show that the non-preemptiveness introduced by quantum-based scheduling can improve the schedulability of fixed priority tasks, and there is a task set which is not schedulable by preemption threshold scheduling but is schedulable by quantum-based scheduling. This paper also presents a method to calculate the worst case response time of tasks in quantum-based scheduling.