Mapping and Scheduling Mixed-Criticality Systems with On-Demand Redundancy

Embedded systems in several domains such as avionics and automotive are subject to inspection from certification authorities. These authorities are interested in verifying the safety-critical aspects of a system and, typically, do not certify non-critical parts. The design of such Mixed-Criticality Systems (MCS) has received increasing attention in recent years. However, although MCS must be designed to overcome transient faults, their susceptibility to transient faults is often overlooked. In this paper, we consider the problem of mapping and scheduling efficient, certifiable MCS that can survive transient faults. We generalize previous MCS models and analysis to support On-Demand Redundancy (ODR). A task set transformation is proposed to generate a modified task set that supports various forms of ODR while satisfying reliability and certification requirements. The analysis is incorporated into a design space exploration algorithm that supports a wide range of fault-tolerance mechanisms and heterogeneous platforms. Experiments show that ODR can improve Quality of Service (QoS) provided to non-critical tasks by 29 percent on average, compared to lockstep execution. Moreover, combining several fault-tolerance mechanisms can lead to additional improvements in schedulability and QoS.