Performance of algorithms for scheduling real-time systems with overrun and overload

This paper compares the performance of three classes of scheduling algorithms for real-time systems in which jobs may overrun their allocated processor time potentially causing the system to be overloaded. The first class, which contains classical priority scheduling algorithms as exemplified by DM and EDF, provides a baseline. The second class is the Overrun Server Method which interrupts the execution of a job when it has used its allocated processor time and schedules the remaining portion as a request to an aperiodic server. The final class is the Isolation Server Method which executes each job as a request to an aperiodic server to which it has been assigned. The performance of the Overrun Server and Isolation Server Methods are worse, in general, than the performance of the baseline algorithms on independent workloads. However, under the dependent workloads considered, the performance of the Isolation Server Method, using a server per task scheduled according to EDF, was significantly better than the performance of classical EDF.