Evaluation of Fault-Tolerant Multiprocessor Systems for High Assurance Applications

Abstract

In designing high assurance systems, the dependability goals are achieved through the adoption of several fault tolerance techniques. Unfortunately, their combined effect on the system cannot be, in the general case, derived by straightforward composition of the stand-alone component's analysis, because of mutual dependence of their controlling parameters. In this paper the assessment of overall system dependability induced by such integrated fault tolerance organizations is carried out through a stochastic simulation approach. To this purpose, a few fault tolerant multiprocessor architectures, based on the integrated usage of standard error processing structures with a recently proposed diagnostic mechanism, called -count, are selected and evaluated. The diagnostic mechanism gets its input (error signals) from the error processing mechanism, whose behaviour is in turn influenced by the rapidity and correctness with which -count identifies permanently/intermittently faulty processors. The choice of the basic fault tolerance mechanisms to adopt, as well as the reference system architecture, has been driven by the characteristics of the envisaged target applications: mainly, stringent dependability requirements, to be traded with adequate levels of performance and cost. The analysis has been focused on performability, which is an appropriate measure to evaluate whether a certain design is "better" than another under dependability and performance point of view.