Modified Rate-Monotonic Algorithm for Scheduling Periodic Jobs with Deferred Deadlines

Abstract

The deadline of a request is the time instant at which its execution must complete. The deadline of the request in any period of a job with deferred deadline is some time instant after the end of the period. This paper describes a semi-static priority-driven algorithm for scheduling periodic jobs with deferred deadlines: each job is assigned two priorities, the higher one for old requests and the lower one for the current request. This algorithm is called the modified rate-monotonic algorithm and is based on the well-known rate-monotonic algorithm. We show that the modified rate-monotonic algorithm is optimal when the deadline of every job is deferred by max (1, 7 - 1) periods or more, where 7 is the ratio between the longest period and the shortest period. When the deadline of each job is deferred by one period of the job, any set of n independent jobs whose total utilization is equal to or less than [1 + n(21u - 1)]/2 can be feasibly scheduled by this algorithm. This bound approaches 0.845 when n approaches infinity. © 1993 IEEE