EDF Scheduling for Tasks with Uncertain Execution Times in Networked Control System

The execution times of the real-time tasks are uncertain in the networked control system. So the classical scheduling algorithms are not suitable for deciding the priorities of tasks. On the basis of the classical EDF, this paper proposes the static extension EDF scheduling algorithm according to the uncertainty of the execution times. This algorithm can get the distribution function of the schedulability variable according to the distribution functions of tasks with the fuzzy theory. Then the value of schedulability variable which is satisfied the scheduling of the system can be determined by the possibility and necessity of the schedulability variable. The suitable execution time of each task can be calculated to decide the priority of each task. So the order of data can be decided. This algorithm is very simple and overcomes the disadvantage of not deciding priority by fuzzy time in classical scheduling algorithm. Also, it keeps the advantage of high occupancy rate of the resources. It is proved that this algorithm can schedule well under uncertainty.