A Fault-Tolerant Dynamic Scheduling Algorithm for Multiprocessor Real-Time Systems and Its Analysis

Many time-critical applications require dynamic scheduling with predictable performance. Tasks corresponding to these applications have deadlines to be met despite the presence of faults. In this paper , we propose an algorithm to schedule dynamically arriving real-time tasks with resource and fault-tolerant requirements on to multiprocessor systems. The tasks are assumed to be non-preemptable and each task has two copies (versions) which are mutually excluded in space as well as in time in the schedule, to handle permanent processor failures and to obtain better performance, respectively. Our algorithm can tolerate more than one fault at a time, and employs performance improving techniques such as (i) distance concept which decides the relative position of the two copies of a task in the task queue, (ii) exible backup overloading, which introduces a tradeoo between degree of fault-tolerance and performance, and (iii) resource reclaiming, which reclaims resources both from deallocated backups and early completing tasks. We quantify, through simulation studies, the effectiveness of each of these techniques in improving the guarantee ratio, which is deened as the percentage of total tasks, arrived in the system, whose deadlines are met. Also, we compare through simulation studies the performance our algorithm with a best known algorithm for the problem, and show analytically the importance of distance parameter in fault-tolerant dynamic scheduling in mul-tiprocessor real-time systems.