Extending a Task Allocation Algorithm for Graceful Degradation of Real-Time Distributed Embedded Systems

Previous research which has considered task allocation and fault-tolerance together has concentrated on construct-ing schedules which accommodate a fixed number of redun-dant tasks. Often, all faults are treated as being equally severe. There is little work which combines task allocation with architectural level fault-tolerance issues such as the number of replicas to use and how they should be config-ured, both of which are tackled by this work. An accepted method for assessing the impact of a combination of faults is to build a system utility model which can be used to assess how the system degrades when components fail. The key challenge addressed here is how to design objective func-tions based on a utility model which can be incorporated into a search algorithm in order to optimise fault-tolerance properties. Other issues such as how to extend the local search neighbourhood and balance objectives with schedu-lability constraints are also discussed.