Task Scheduling Algorithms for Fault Tolerance in Real-time Embedded Systems

We survey scheduling algorithms proposed for tolerating permanent and transient failures in real-time embedded systems. These algorithms attempt to provide low-cost solutions to fault tolerance, graceful performance degradation, and load shedding in such systems by exploiting tradeoffs between space and/or time redundancy, timing accuracy, and quality of service. We place fault-tolerant scheduling algorithms in three broad categories: dynamic scheduling, off-line or static scheduling, and scheduling of imprecise computations. Under dynamic scheduling, we survey faulttolerance extensions to the widely used rate-monotonic and earliestdeadline-first scheduling policies. We then discuss methods that provide fault tolerance in statically scheduled systems using precomputed alternate schedules or run-time rescheduling. We also discuss imprecise scheduling, which achieves a tradeoff between solution quality and timeliness. We conclude with a brief discussion of scheduling and fault-tolerance issues related to safety-critical embedded systems.