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Earliest Deadline First (EDF) is the most widely studied optimal dynamic scheduling algorithm for uniprocessor real-time systems. For realistic programs, tasks must be allowed to exchange data and use other forms of resources that must be accessed under mutual exclusion. With EDF scheduled systems, access to such resources is usually controlled by the use of Baker's Stack Resource Protocol (SRP). In this paper we propose an alternative scheme based on deadline inheritance. Shared resources are assigned a relative deadline equal to the minimum (floor) of the relative deadlines of all tasks that use the resource. On entry to the resource a task's current absolute deadline is subject to an immediately reduction to reflect the resource's deadline floor. On exit the original deadline for the task is restored. We show that the worst-case behaviour of the new protocol (termed DFP-Deadline Floor inheritance Protocol) is the same as SRP. Indeed it leads to the same blocking term in the scheduling analysis. We argue that the new scheme is however more intuitive, removes the need to support preemption levels and we demonstrate that it can be implemented more efficiently.

Modern industrial cyberphisical systems exhibit increasingly complex execution patterns like multipath endto-end flows, that force the real-time community to extend the schedulability analysis methods to include these patterns. Only then it is possible to ensure that applications meet their deadlines even in the worstcase scenario. As a driving motivation, we present a real industrial application with safety requirements, that needs to be re-factored in order to leverage the features of new execution paradigms such as time partitioning. In this context we develop a new response-time analysis technique that provides the capacity of obtaining the worst-case response time of multipath flows in time-partitioned hierarchical schedulers and also in general fixed-priority (FP) real-time systems. We show that the results obtained with the new analysis reduce the pessimism of the currently used holistic analysis approach. INDEX TERMS Schedulability analysis, time partitioning, hierarchical scheduling, distributed systems, safety, industrial application.

Abstract:A framework for application-defined scheduling and its corresponding application program interface (API) were defined during the last International Real-Time Ada Workshop, and are being proposed for standardization in the future revision of the Ada language. The framework allows applications to install one or more task schedulers capable of implementing a large variety of scheduling algorithms. This paper describes the implementation of this framework, both at the compiler and the run-time system levels. The objective of this work is to serve as a reference implementation in which the API can be evaluated and tested, and its performance can be assessed. We show that the amount of changes to the compiler is relatively small, and that the application scheduling capability can be supported with a small level of complexity.

<p>En las últimas tres décadas, se ha realizado un gran número de propuestas sobre la optimización del despliegue y planificación de sistemas de tiempo real distribuidos bajo diferentes enfoques algorítmicos que aportan soluciones aceptables a este problema catalogado como NP-difícil. En la actualidad, la mayor parte de los sistemas utilizados en el sector industrial son sistemas de criticidad mixta en los que se puede usar la planificación cíclica, las prioridades fijas y el particionado, que proporciona aislamiento temporal y espacial a las aplicaciones. Así, en este artículo se realiza una revisión de los trabajos publicados sobre este tema y se presenta un análisis de las diferentes soluciones aportadas para sistemas de tiempo real distribuidos basados en las políticas de<br />planificación que se están usando en la práctica. Como resultado de la comparación, se presenta una tabla a modo de guía en la que se relacionan los trabajos revisados y se caracterizan sus soluciones.</p>

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The Ada 2005 standard introduced "Earliest Deadline First" (EDF) as one of the supported dispatching policies. The standard specifies the "Stack Resource Protocol" (SRP) as the protocol for resource sharing among EDF tasks. During the time the SRP has been in the standard it has shown to be a relatively complex protocol. Recently, a new protocol has been proposed for resource sharing in EDF. This new protocol, called "Deadline Floor inheritance Protocol" (DFP), is simpler and more efficient than SRP while keeping all its good properties. In this paper we briefly describe both protocols and compare them from the complexity point of view. In light of its simplicity, we propose to change the language standard to include DFP instead of SRP. Some alternative modifications of the Ada Reference Manual are pointed out in order to include DFP in the most straightforward way.

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