Resource augmentation for fault-tolerance feasibility of real-time tasks under error bursts

Abstract

Dependability is a vital system requirement, particularly in safety critical and mission critical real-time systems, due to the potentially catastrophic consequences of failures. In most critical applications different fault tolerance mechanisms using redundancy are employed to prevent possible failures. In the case of real-time systems the system designer must ensure that the task set is feasible even under faults, which we refer to as 'fault tolerance feasibility'. Due to cost considerations, often temporal redundancy has been prevalently used to meet this objective. In this paper we focus on guaranteeing fault-tolerance feasibility under error bursts on uni-processor systems by the usage of resource augmentation, specifically through processor speed-up. Firstly, we derive a processor demand bound based sufficient condition for a set of real-time tasks to be fault tolerance feasible under an assumption that no more than one error burst occurs during the hyper-period of the task set. Subsequently, we derive the necessary resource augmentation bounds (i.e., the processor speed-up), that guarantees the fault tolerance feasibility, if the sufficient test fails. Finally, we prove that, if the error burst length is no more than half the shortest relative deadline of the task set, the minimum processor speed-up required to guarantee fault tolerance feasibility is upper-bounded by 6.

A Real-Time Performance Monitoring Tool for Dual Redundant and Resource Augmented Framework of Cruise Control System

“…A resource augmentation bounds on the processor speed-up required for a fixed priority scheduler to schedule all the task sets scheduled by an optimal scheduling algorithm was also derived by Davis. Abilash et.al., [12] focused on guaranteeing fault tolerance under error bursts on uni-processor systems by resource augmentation. A novel paradigm for fault tolerance of a permanent fault is explained in detail in [13,14,15], using task level criticality for redundancy.…”

“…Dependability is a vital system requirement, in safety critical due to the potentially catastrophic consequences of failures [12]. Dependability of the system is typically achieved by use of fault tolerance mechanism using redundancy, which involves the execution of tasks on both primary and redundant units.…”

“…It is very difficult to predict such faults. Transient faults appear and disappear quickly, they are mainly due to random environmental disturbances such as EMI [12]. In realtime safety-critical systems fault tolerance is typically provided by redundancy either hardware or software or both.…”

Real-time scheduling under fault bursts with multiple recovery strategy

“…Existing studies assume that the upper bound on the duration of the fault burst (∆) is available in advance [8], [9]. This value is in general domain-specific and its derivation may require input from domain experts.…”

“…In a real system, the fault burst can occur at any time. As the existing efforts on settings with fault bursts emphasize [8], [9], [11] , when a fault is detected, the scheduler has no way of knowing when exactly the burst has started. This makes optimal recovery decisions very challenging.…”