Escalonamento dinamico de tarefas periodicas e esporadicas

AUTOR(ES)

Sibelius Lelis Vieira

DATA DE PUBLICAÇÃO

1994

RESUMO

Nowadays, the design and implementation of Hard Real-Time(HRT) Systems can only be accomplished through a formal methodological approach. These HRT systems are based upon the fact that the quantitative temporal behaviour must be meto Otherwise, severe negative consequences may occur and be spread in the environment. Such behaviour is due to the fact that HRT systems are, generally, embebbed in larger systems that control physical processes. This work is closely tied to the fiexibility and predictability paradigm. This paradigm requires that the HRT system must be fiexible enough to adapt to its environment, and, at the same time, that the desired behaviour will be guaranteed to occur, insuring a safe system. Flexibility relates itself to dynamic reconfiguration( on-line), while predictability will guarantee that the behaviour is according to what is expected. In this way, these aspects may confiict with each other. In this work, we search for schedulability tests that are suitable when dealing with dynamic environment HRT systems. Thus, we allow systems whose comimtational tasks might have varying parameters, for example, variable worst case execution time. The research core contributes to the scheduling theory of periodic and sporadic tasks, particularly when on-line tests are necessary. It will be seen several scheduling models of periodic and sporadic tasks, from the very simple assumptions, where tasks are independent and completely preemptible, up to cases where precedence relations occurs. Initially, we investigate the schedulability of a periodic task set with arbitrary deadlines, through the utilization factor. We propose a schedulability test that is suitable to online scheduling. Then, we drift to a dynamic sporadic server, that can be used as a schedulability test at execution time, and we provide a suflicient condition for sporadic test scheduling as well as redesign an exact condition in order to fullfill the timetable. Through the simulations, we analyse how accurate our condition is working. In order to guarantee that the most important sporadic tasks will met their temporal constraints, even operating at overload, we propose a scheduling algorithm that will try to guarantee important tasks and not to jeopardize urgent tasks. We show that our algorithm is computationally fast and has a great eflicient average. Finally, we deal with periodic tasks that present precedence relations, such that they can be embebbed in a system with sporadic and independent periodic tasks and the overall schedulability may be tested on-line. So, our thesis is very concerned about fiexible environments, as we employ on-line tests, as well as predictable issues, dictated by the applications

ASSUNTO(S)

sistemas de tempo real

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