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 constructing schedules which accommodate a fixed number of redundant 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 configured, 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 functions 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 schedulability constraints are also discussed.