Abstract
Scheduling problems vary widely in the nature of their constraints and optimization criteria. Most scheduling algorithms make restrictive assumptions about the constraints and criteria and hence are applicable to only a limited set of scheduling problems. A reconfigurable scheduler is one that, unlike most schedulers, is easily configured to handle a wide variety of scheduling problems with different types of constraints and criteria. We have implemented a reconfigurable scheduler, called Vishnu, that handles an especially large range of scheduling problems. Vishnu is based upon a genetic algorithm that feeds task orderings to a greedy scheduler, which in turn allocates those tasks to a schedule. The scheduling logic (i.e. constraints and optimization criteria) is reconfigurable, and Vishnu includes a general and easily expandable framework for expressing this logic using hooks and formulas. The scheduler can find an optimized schedule for any problem specified in this framework. We illustrate Vishnu's flexibility and evaluate its performance using a variety of scheduling problems, including some classic ones and others from real-world scheduling projects.