D-OVER ; an optimal on-line scheduling algorithm for overloaded real-time systems
Abstract
Every task in a real-time system has a deadline by which time it should complete. Each task also has a value that it obtains only if it completes by its deadline. The problem is to design an on-line scheduling algorithm (i.e., the scheduler has no knowledge of a task until it is released) that maximizes the obtained value. When such a system is underloaded (i.e. there exists a schedule for which all tasks meet their deadlines), Dertouzos showed that the earliest deadline first algorithm will achieve 100% of the possible value. Locke showed that earliest deadline firtst performs very badly when the system is overloaded and proposed heuristics to deal with overload. This paper presents an optimal on-line scheduling algorithm for overloaded systems. It is optimal in the sense that it gives the best competitive factor possible relative to an offline scheduler.