A Mixed-Criticality Approach to Fault Tolerance: Integrating Schedulability and Failure Requirements

Mixed-Criticality (MC) systems have been widely studied in the past decade, majorly due to their potential to consolidate applications with different criticality levels onto the same platform. In the original design proposed by Vestal, a target probability of failure per hour specified by certification requirements is assigned to each criticality level. These requirements have been mainly conceived for hardware faults. Software fault tolerance techniques are available to mitigate hardware faults, but their adaptation to real-time systems is challenging due to the introduced overhead. This paper proposes an extension to the traditional MC scheduling theory to implement fault tolerance strategies against transient faults, with the goal of complying with both failure and timing requirements. In particular, we introduce the dropping relationships that generalize the concept of criticality and allow, on the one hand, to improve the schedulability analysis, on the other, to control the dependency between tasks satisfying the certification requirements. The simulation study shows a schedulability ratio improvement of 20-30% compared to classical scheduling while maintaining compliance with failure requirements.