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Fixed priority schedulers are widely used for real-time systems, and there were efforts to improve the schedulability. Preemption threshold scheduling is one of such efforts with a dual priority scheme. It increases the schedulability by introducing priority inversion during task execution. In this paper, we analyze another scheduling model, quantumbased scheduling. When quantum-based scheduling is combined with priority-based scheduling, the quantum introduces a partially non-preemptive region. 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 presents a method to calculate the worst case response time of tasks in quantum-based scheduling. Based on the previous research results for preemptive and non-preemptive scheduling, we present a priority assignment method for quantum-based scheduling also.

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