Optimal scheduling of cooperative tasks in a distributed system using an enumerative method

Preemptive (resume) scheduling of cooperative tasks that have been preassigned to a set of processing nodes in a distributed system, when each task is assumed to consist of several modules is discussed. During the course of their execution, the tasks communicate with each other to collectively accomplish a common goal. Such intertask communications lead to precedence constraints between the modules of different tasks. The objective of this scheduling is to minimize the maximum normalized task response time, called the system hazard. Real-time tasks and the precedence constraints among them are expressed in a PERT/CPM form with activity on arc (AOA), called the task graph (TG), in which the dominance relationship between simultaneously schedulable modules is derived and used to reduce the size of the set of active schedules to be searched for an optimal schedule. Lower-bound costs are estimated, and are used to bound the search. An example of the task scheduling problem and some computational experiences are presented