Fault-Tolerant Scheduling Based on Periodic Tasks for Heterogeneous Systems

Abstract

Most existing real-time fault-tolerant scheduling algorithms for heterogeneous distributed systems can achieve high reliability for non-preemptive and aperiodic tasks. However, the existing scheduling algorithms assume that status of each backup copy is either active or passive. To remedy this deficiency, we propose a novel reliability model tailored for preemptive periodic tasks. Next, we develop two real-time fault-tolerant algorithms (NRFTAHS and RDFTAHS) for heterogeneous distributed systems. NRFTAHS manages to assign tasks in a way to improve system schedulabilties, whereas RDFTAHS aims at boosting system reliability without adding extra hardware. Unlike the existing scheduling schemes, our algorithms consider backup copies in both active and passive forms. Therefore, our approaches are more flexible than the alternative ones. Finally, we quantitatively compare our schemes with two existing algorithms in terms of performability measured as a function of schedulability and reliability. Experiments results show that RDFTAHS substantially improves the overall performance over NRFTAH.