A practical approach to preemptable and nonpreemptable task scheduling with resource constraints based on earliest deadlines

All intrinsic properties of the earliest-deadline task scheduling discipline are compiled and discussed to show that this is the most advantageous scheme available, characterized by efficiency and allowing for predictable system behavior. It is pointed out how the method naturally extends to the scheduling of tasks having nonpreemptable regions due to resource access constraints. A sufficient condition is derived which allows one, at any arbitrary point in time and under observation of resource constraints, to check the feasible executability of the tasks competing for processor allocation. This condition takes the lengths of the tasks´ critical regions into account and resembles the necessary and sufficient conditions holding for the executability in the case of always preemptable tasks. It reduces to the latter if there are no critical regions, but applies to entirely nonpreemptable tasks as well. The favorable consequences of deadline scheduling for virtual storage management are discussed