Workload redistribution for fault-tolerance in a hard real-time distributed computing system

IEEE Trans. Parallel Distrib. Syst.

1997

163

166

Real-time systems are being increasingly used in several applications which are time critical in nature. Fault-tolerance is an important requirement of such systems, due to the catastrophic consequences of not tolerating faults. In this paper, we study a scheme that provides fault-tolerance through scheduling in real-time multiprocessor systems. We schedule multiple copies of dynamic, aperiodic, nonpreemptive tasks in the system, and use two techniques that we call deallocation and overloading to achieve high acceptance ratio (percentage of arriving tasks scheduled by the system). This paper compares the performance of our scheme with that of other fault-tolerant scheduling schemes, and determines how much each of deallocation and overloading affects the acceptance ratio of tasks. The paper also provides a technique that can help real-time system designers determine the number of processors required to provide fault-tolerance in dynamic systems. Lastly, a formal model is developed for the analysis of systems with uniform tasks.

Section: Related Workmentioning

confidence: 99%

Fault-tolerance through scheduling of aperiodic tasks in hard real-time multiprocessor systems

Ghosh

IEEE Trans. Parallel Distrib. Syst.

1997

163

166

“…3 When this start timer goes off, the thread is placed in the run queue of priority 0. To simplify and shorten the time of handling the timeline, we reduce the number of timers armed by enforcing that only the thread at the head of the queue has armed timers.…”

Section: Adding the Timeline To Rt Machmentioning

confidence: 99%

“…Balaji et al [3] present a best effort approach to provide fault-tolerance in hard real-time distributed computing systems. A primary/backup scheme is used in which both the primary and the backup start execution simultaneously and if a fault affects the primary, the results of the backup are used.…”

Section: Related Workmentioning

confidence: 99%

A nonpreemptive real-time scheduler with recovery from transient faults and its implementation

IIEEE Trans. Software Eng.

Ghosh

2003

Abstract-Real-time systems (RTS) are those whose correctness depends on satisfying the required functional as well as the required temporal properties. Due to the criticality of such systems, recovery from faults is an essential part of a RTS. In many systems, such as those supporting space applications, single event upsets (SEUs) are the prevalent type of faults; SEUs are transient faults and affect a single task at a time. This paper presents a scheme to guarantee that the execution of real-time tasks can tolerate SEUs and intermittent faults assuming any queue-based scheduling technique. Three algorithms are presented to solve the problem of adding fault tolerance to a queue of real-time tasks by reserving sufficient slack in a schedule so that recovery can be carried out before the task deadline without compromising guarantees given to other tasks. The first algorithm is a dynamic programming optimal solution, the second is a linear-time heuristic for scheduling dynamic tasks, and the third algorithm comprises extensions to address queues with gaps between tasks (gaps are caused by precedence, resource, or timing constraints). We show through simulations that the heuristics closely approximate the optimal algorithm. Finally, the paper describes the implementation of the modified admission control algorithm, the nonpreemptive scheduler, and a recovery mechanism in the FT-RT-Mach operating system.

“…Earlier work dealing with tolerance to transient faults for aperiodic tasks was carried out from the perspective of a single fault in the system [16], [14]. More recently, the fault models were enhanced to encompass a single fault occurring every interval of time, for both uniprocessors and multiprocessor systems [1], [6], [7]. Further, tolerance to transient faults for periodic tasks has also been addressed for uniprocessors [26], [27], [22], [24], [8] and multiprocessor systems [2], [23], [19].…”

Section: Related Workmentioning

confidence: 99%

“…In [1], a best effort approach to provide fault tolerance has been discussed in hard real-time distributed systems. A primary/backup scheme is used in which both the primary and the backup start execution simultaneously and if a fault affects the primary, the results of the backup are used.…”

Section: Related Workmentioning

confidence: 99%

Tolerance to multiple transient faults for aperiodic tasks in hard real-time systems

Liberato

2000

IEEE Trans. Comput.

ÐReal-time systems are being increasingly used in several applications which are time-critical in nature. Fault tolerance is an essential requirement of such systems, due to the catastrophic consequences of not tolerating faults. In this paper, we study a scheme that guarantees the timely recovery from multiple faults within hard real-time constraints in uniprocessor systems. Assuming earliestdeadline-first scheduling (EDF) for aperiodic preemptive tasks, we develop a necessary and sufficient feasibility-check algorithm for fault-tolerant scheduling with complexity yn P Á k, where n is the number of tasks to be scheduled and k is the maximum number of faults to be tolerated. Index TermsÐReal-time scheduling, earliest-deadline first, fault-tolerant schedules, fault recovery.