Aperiodic task scheduling for Hard-Real-Time systems

Abstract

Abstract.A real-time system consists of both aperiodic and periodic tasks. Periodic tasks have regular arrival times and hard deadlines. Aperiodic tasks have irregular arrival times and either soft or hard deadlines. In this article, we present a new algorithm, the Sporadic Server algorithm, which greatly improves response times for soft deadline aperiodic tasks and can guarantee hard deadlines for both periodic and aperiodic tasks. The operation of the Sporadic Server algorithm, its performance, and schedulability analysis are discussed and compared with previously published aperiodic service algorithms.

A Hierarchical Scheduling Approach for Symmetric Multiprocessing Based Real Time Systems on VxWorks

“…Our hierarchical scheduling framework is based around the periodic resource model [5] and [20]. Similar to [20], 23]- [24] , we have implemented the periodic resource model by the usage of a server based approach that replenish their budget every constant period, i.e., the servers behave like periodic tasks.…”

Scheduling Jobs with Multiple Feasible Intervals

“…Thus far, and in our subsequent discussion, we use the term task and job as they are commonly used in real-time systems literature [6,7,8]. A job is an instance of computation, or the transmission of a data packet, or the retrieval of a file, and so on.…”

Real-Time System Scheduling

“…This is termed the deferrable server 43,66,70 . When the server is run with no outstanding non-periodic process requests, the server does not execute but defers its assigned computation time.…”

“…Both algorithms provide better response time than a conventional polling approach 43 . The sporadic server algorithm 70,66 combines the advantages of the above two algorithms. This is achieved by varying the points at which the computation time of the server is replenished, rather than merely at the start of each server period.…”