Task-level Redundancy vs Instruction-level Redundancy against Single Event Upsets in Real-time DAG scheduling

Real-time cyber-physical systems have become ubiquitous. As such systems are often mission-critical, designers must include mitigations against various types of hardware faults, including Single Event Upsets (SEU). SEUs can be mitigated using both software and hardware approaches. When using software approaches, the application designer needs to select the appropriate redundancy level for the application. We propose the use of task-level redundancy for SEU detection, aiming at applications structured as a Directed Acyclic Graph (DAG) of tasks. This work compares existing instruction-level redundancy against task-level redundancy using the UPPAAL model checking tool in SMC mode. Our comparison shows that task-level redundancy implemented using Dual Modular Spatial Redundancy and Checkpoint-Restart offers significantly lower deadline miss ratios when slack is limited. While task-level redundancy usually performs better or equal, we also show that rare cases exist where long running DAG application benefit more from instruction-level redundancy.