Allocation of real-time computations under fault tolerance constraints

Abstract

Allocation of resources in ''next-generation" real-time operating systems requires some important features in addition to those demonstrated by current systems, resulting in an increased complexity of each system. The allocation is closely related to the scheduling, and the two are based on time considerations, rather then on a static priority scheme. The allocation is fault tolerance motivated, to cope with the application's reliability goals. Distributed system issues and adaptive behavior requirements increase the complexity and significance of the allocation approach.The allocation scheme we propose here accomplishes the hard real-time goal of guaranteeing a deadline satisfaction in case the job is accepted. In addition, this allocation scheme supports fault tolerance objectives in both damage containment and resiliency requirements. It does this in cooperation with a schedulability verification mechanism, and with an object architecture in which for each object there exists a calendar that maintains the time of its execution. A nice feature of this scheme is the way in which it can be used for reallocation while increasing the resiliency.

Real-Time System Scheduling

“…25 , (ii) the concurrency of the system, (iii) fault-tolerant considerations 48 , and (iv) relative periods. The cost of accessing resources or performing inter-process interactions is clearly more expensive for remote operations.…”

High integrity software for nuclear power plants: Candidate guidelines, technical basis and research needs. Main report, Volume 2

“…This approach to software design has two main safety benefits: (1) it minimizes the ripple effect of design changes in a component on related components, and (2) it minimizes the propagation of abnormal conditions to a few neighboring components (Le., validating input at the interface to detect erroneous data). In addition, a modular design is easier to understand because it divides the problem into a manageable set of interrelated components pooch, 1991;Meyer, 19881 is one of the most important issues in real-time operating systems" [Levi andAgrawala, 1990: p. 1671. Also, the encapsulation of external interfaces allows data validation and error processing to occur before the event is communicated to other components.…”

“…One approach to achieving this objective is to protect the validity of the data used by the software. Although data integrity is an important concern in all application areas, it is considered one of the most important areas to be addressed in designing real-time software [Gehani and McGettrick, 1988;Levi and Agrawala, 19901 and database management systems mutt, 19921.…”

“…From [Littlewood, 19911: "The failure rate for certification of the French-developed Airbus avionics is required to be no greater than 104 failureshour. "…”