A Comparative Study of System-Level Energy Management Methods for Fault-Tolerant Hard Real-Time Systems

Low energy consumption and fault tolerance are often key objectives in the design of real-time embedded systems. However, these objectives are at odds, and there is a trade-off between them. Real-time systems usually use system level energy reduction methods, i.e., dynamic voltage scaling (DVS) and dynamic power management (DPM). Also hard real-time systems often use replication to achieve fault tolerance. In this paper, we investigate the impact of system level energy reduction methods on both the reliability and energy consumption of hard real-time systems which use replication for fault tolerance. In this analysis, we have considered four various existing energy management methods: 1) Classic DPM, 2) Classic DVS, 3) Postponement method: a variation of DPM which is only applicable to replicated systems, and 4) Hybrid method: a combination of Postponement and DVS. Based on the comparative study, we have provided guidelines so that a designer can decide which energy management method is more suitable for a given application. For example, we have shown that when reliability is the main concern, the postponement method is the most preferable. However, when the energy consumption is the primary concern, the hybrid method may be more appropriate.