A Note on the EDF Preemption Behavior in "Rate Monotonic Versus EDF: Judgment Day"

In [1], the author empirically compared EDF (Earliest Deadline First) and RM (Rate Monotonic) scheduling algorithms and made a few EDF preemption behavior observations based on data obtained from the first 1,000 time units of scheduling activities. However, based on test settings given in [1], the first 1,000 time units occupies only a small percentage of the entire task set’s hyper-period. We extend EDF preemption behavior study by extending scheduling activities from the first small percentage of a hyper-period of a given task to the entire hyper-period. The extended experiments indicate that the number of preemptions occurred at the beginning of a task set’s hyper-period does not necessarily represent the trend for the entire hyper-period. Hence, comparisons and conclusions made based on a small percentage of a scheduling interval over a task set’s hyper-period may not be accurate. Second, the total number of preemptions within a task set’s hyper-period does not decrease when the task set total utilization increases which is different from the observation obtained in [1]. We also investigate the impact of execution time differences among tasks on the preemption behavior.