A Sufficient Condition for Rate Monotonic Schedulability Based on Response Time Analysis

Abstract

Rate Monotonic scheduling algorithm is widely used in real-time systems and embedded systems for its implementation simplicity and optimality in fixed priority scheduling. Since determining the schedulability of a task set in Rate Monotonic scheduling is an important step in designing a real-time system, schedulability analysis has been extensively studied. Although there is an exact schedulability test method for Rate Monotonic scheduling, the exact test is too complex to be executed on-line for large number of tasks because it is based on the response time calculation which is NP-hard. Thus many researchers studied on polynomial time sufficient conditions on Rate Monotonic schedulability. The existing polynomial time sufficient conditions are in the form of a utilization bound; that is, if a task set's total utilization is not larger than a utilization bound, the task set is accepted as schedulable one. Though the utilization bound tests are simple, they suffer from poor processor utilization. In this paper, we propose a new sufficient schedulability condition based on the response time test, different from the previous approaches. The new test provides a condition that is both necessary and sufficient for task sets with period ratio less than 2, while the previous tests provide only sufficient conditions. Extensive simulations show that our test significantly outperforms the existing tests with utilization bound.