Greed in resource scheduling

An examination is made of the worst-case performance of a class of scheduling algorithms commonly known as priority-driven or list-scheduling algorithms. These algorithms have anomalous, unpredictable performance when used to suboptimally schedule nonpreemptive tasks with precedence constraints. A general method is presented for deriving the worst-case performance of these algorithms. This method is easy to use, yet powerful enough to yield tight performance bounds for many classes of scheduling problems. It is demonstrated that the method has wide applicability. Several task systems are presented for which list-scheduling algorithms have worst-case performance, and the general characteristics of these task systems are discussed. It is believed that these task systems are sometimes ignored in simulation studies; consequently, the results of these studies may be overly optimistic