The rejection rate for tasks with random arrivals, deadlines, and preemptive scheduling

A means of approximating light-traffic performance of RAD (random-arrivals-with-deadlines) systems for four basic preemptive scheduling policies is presented. The design goal is to keep congestion low enough to make the probability of rejection acceptably small. These designs must have low processor utilization. The study analyzes rejection probabilities at utilizations up to 20% and rejection probabilities up to about 10% for various well-known preemptive scheduling disciplines (shortest job first, earliest due date, and least laxity first), as well as first-come, first-served. Good approximations for the rejection probability and for a number of other properties, such as the distribution of time-to-go at rejection, are found