Priority Assignment Algorithm Research Articles

An optimal fixed-priority assignment algorithm for supporting fault-tolerant hard real-time systems

The main contribution of this paper is twofold. First, we present an appropriate schedulability analysis, based on response time analysis, for supporting fault-tolerant hard real-time systems. We consider systems that make use of error-recovery techniques to carry out fault tolerance. Second, we propose a new priority assignment algorithm which can be used, together with the schedulability analysis, to improve system fault resilience. These achievements come from the observation that traditional priority assignment policies may no longer be appropriate when faults are being considered. The proposed schedulability analysis takes into account the fact that the recoveries of tasks may be executed at higher priority levels. This characteristic is very important since, after an error, a task certainly has a shorter period of time to meet its deadline. The proposed priority assignment algorithm, which uses some properties of the analysis, is very efficient. We show that the method used to find out an appropriate priority assignment reduces the search space from O(n!) to O(n/sup 2/), where n is the number of task recovery procedures. Also, we show that the priority assignment algorithm is optimal in the sense that the fault resilience of task sets is maximized as for the proposed analysis. The effectiveness of the proposed approach is evaluated by simulation.

Point-to-Point Real-Time Communication Over a Backplane Bus

This paper suggests two scheduling methods for a real-time point-topoint communication over a backplane bus which has limited priorities for the bus mastership. Fixed priority assignment(FPA) algorithm based on the rate monotonic scheduling is suggested for the periodic hard real-time applications. Dynamic priority assignment(DPA) algorithm based on the earliest deadline first scheduling is suggested for the sporadic soft real-time applications. The worst communication latency for the proposed methods is analyzed and then the schedulability is evaluated using computer simulation.

Design algorithm for packet‐switching networks with different classes of packets‐capacity, priority, and flow assignment under endto‐end packet delay constraint

AbstractThis paper proposes a design algorithm for packet‐switching networks with different classes of packets under end‐to‐end packet delay constraint and a design algorithm for fault‐tolerant networks. the former is a heuristic capacity, priority, and flow assignment algorithm which locally minimizes the network cost while satisfying a constraint that the average transmission delay of each class of packets between two arbitrary nodes never exceed a value predetermined for the class.This algorithm is composed of three subalgorithms and the cost minimization is pursued by iterating these algorithms as long as the constraint is satisfied. the latter is a design algorithm for a fault‐tolerant network which satisfies the foregoing constraint even if an arbitrary single link fails. With this algorithm, an assignment with relatively large cost but satisfying the constraint is obtained first. Then a procedure of reducing the capacity of a link whose effect on cost reduction is great but whose effect on path delay increase is not so great is iterated to reduce the network cost as long as the constraint is satisfied.

Real-time transaction scheduling

Real-time databases are an important component of embedded real-time systems. In a real-time database context, transactions must not only maintain the consistency constraints of the database but must also satisfy the timing constraints specified for each transaction. Although several approaches have been proposed to integrate real-time scheduling and database concurrency control methods, none of them take into account the dynamic cost of scheduling a transaction. In this paper, we propose a new cost conscious real-time transaction scheduling algorithm which considers dynamic costs associated with a transaction. Our dynamic priority assignment algorithm adapts to changes in the system load without causing excessive numbers of transaction restarts. Our simulations show its superiority over EDF-HP algorithm.

Pull versus push strategy for automated guided vehicle load movement in a batch manufacturing system

Most automated guided vehicle (AGV) dispatching rules reported in literature to date are based on the attributes of the vehicles and the workcenters from where the loads originate. These rules can therefore be described as source driven vehicle dispatching rules. In none of these rules is the load pickup priority determined based on the states of the load destinations. Therefore, the priority assignment algorithms used by source driven rules are inflexible for application in some manufacturing systems, especially those based on the just-in-time (JIT) principle. What is required for JIT manufacturing therefore is a demand driven rule. In this paper, an algorithm that assigns load movement priority based on the demand states of the load destinations is presented. When applied to the material flow of an illustrative shop, analysis indicates that the algorithm performs competitively with some of the best source driven rules currently reported. It also provides a material flow and workcenter priority assignment flexibility not matched by any source based rules.

A simulation tool for performance evaluation of the IBM 360/75

In this paper we present some results obtained from using simulation as a tool for evaluating alternative methods of improving system performance in network computers. We begin by describing a GPSS model which was developed to evaluate the current computer center operations at the University of Illinois. While using actual data from the center to verify that the model accurately predicts each job's total time in the system, we evaluate the resource utilization within the center. Then we use the simulator to show that a proposed dynamic priority assignment algorithm yields better throughput than the existing algorithm while maintaining a higher level of CPU and memory utilization. Next, turning our attention to a hypothetical network of three centers, we use a generalization of our model to demonstrate the effects of load leveling between centers on the total system throughput. Here we also explore the merits of “pay-for-priority” schemes in both a single center and in a network of three centers.