QAFT: A QoS-Aware Fault-Tolerant Scheduling Algorithm for Real-Time Tasks in Heterogeneous Systems

Fault-tolerant scheduling, effective means of improving system reliability, plays a significant role in some mission-critical applications. Although extensive fault-tolerant scheduling algorithms have been proposed for real-time tasks in distributed systems, quality of service (QoS) requirements demanded by mission-critical tasks have not been taken into consideration. This paper proposes a QoS-aware fault-tolerant scheduling algorithm named QAFT that can tolerate one processor´s permanent failure at one time instant for real-time tasks with QoS needs in heterogeneous systems. QAFT strives to advance the start time of primary copies and delay the start time of backup copies to make backup copies adopt passive execution scheme or decrease the simultaneous execution time of the primary and backup copies of a task as much as possible to improve resource utilization. Besides, overlapping technology of backup copies is employed. Compared with NOQAFT and DYFARS, QAFT shows obvious superiority to others with higher scheduling quality by simulation experiments.