A new scheduling approach supporting different fault-tolerant techniques for real-time multiprocessor systems

Abstract

Many time-critical applications require predictable performance and tasks in these applications have deadlines to be met even in the presence of faults. Three different approaches have evolved for fault-tolerant scheduling of real-time tasks in multiprocessor systems — Triple Modular Redundancy (TMR), Primary Backup (PB), and Imprecise Computation (IC). In TMR approach, the fault detection is by voting, whereas in PB and IC approaches, it is by acceptance test. The different methods employed for error detection in the three approaches often make one approach preferable to the other in certain applications. Also, some applications can have tasks which require more than one fault-tolerant approach. Hence, it is necessary to have a single fault-tolerant scheduling algorithm which supports different fault-tolerant approaches. Moreover, the redundancy introduced in terms of executing more versions of a task reduces the number of tasks meeting their deadlines (guarantee ratio). In this paper, we address these two issues: (i) by proposing a scheduling algorithm which supports all three fault-tolerant approaches, and (ii) by proposing guarantee ratio improving techniques such as the distance concept and task parallelization, and better algorithms for reclaiming of unused resources at run-time.