Predictability of Earliest Deadline Zero Laxity Algorithm for Multiprocessor Real-Time Systems

Validation methods for hard real-time jobs are usually performed based on the maximum execution time. The actual execution time of jobs are assumed to be known only when the jobs arrive or not known until they finish. A predictable algorithm must guarantee that it can generate a schedule for any set of jobs such that the finish time for the actual execution time is no later than the finish time for the maximum execution time. It is known that any job-level fixed priority algorithm (such as Earliest Deadline First) is predictable. However, job-level dynamic priority algorithms (such as Least Laxity First) may or may not. In this paper, we investigate the predictability of a job-level dynamic priority algorithm EDZL (Earliest Deadline Zero Laxity). We show that EDZL is predictable on the domain of integers regardless of the knowledge of the actual execution times. Based on this result, furthermore, we also show that EDZL can successfully schedule any periodic task set if the total utilization is not greater than (m + 1)/2, where m is the number of processors.