General schedulability bound analysis and its applications in real-time systems

Real-time system refers to the computing, communication, and information system with deadline requirements. To meet these deadline requirements, most systems use a mechanism known as the schedulability test which determines whether each of the admitted tasks can meet its deadline. A new task will not be admitted unless it passes the schedulability test. Schedulability tests can be either direct or indirect. The utilization based schedulability test is the most common schedulability test approach, in which a task can be admitted only if the total system utilization is lower than a pre-derived bound. While the utilization bound based schedulability test is simple and effective, it is often difficult to derive the bound. For its analytical complexity, utilization bound results are usually obtained on a case-by-case basis. In this dissertation, we develop a general framework that allows effective derivation of schedulability bounds for different workload patterns and schedulers. We introduce an analytical model that is capable of describing a wide range of tasks' and schedulers'ÃÂÃÂ behaviors. We propose a new definition of utilization, called workload rate. While similar to utilization, workload rate enables flexible representation of different scheduling and workload scenarios and leads to uniform proof of schedulability bounds. We introduce two types of workload constraint functions, s-shaped and r-shaped, for flexible and accurate characterization of the task workloads. We derive parameterized schedulability bounds for arbitrary static priority schedulers, weighted round robin schedulers, and timed token ring schedulers. Existing utilization bounds for these schedulers are obtained from the closed-form formula by direct assignment of proper parameters. Some of these results are applied to a cluster computing environment. The results developed in this dissertation will help future schedulability bound analysis by supplying a unified modeling framework and will ease the implementation practical real-time systems by providing a set of ready to use bound results

k2U: A General Framework from k-Point Effective Schedulability Analysis to Utilization-Based Tests

To deal with a large variety of workloads in different application domains in real-time embedded systems, a number of expressive task models have been developed. For each individual task model, researchers tend to develop different types of techniques for deriving schedulability tests with different computation complexity and performance. In this paper, we present a general schedulability analysis framework, namely the k2U framework, that can be potentially applied to analyze a large set of real-time task models under any fixed-priority scheduling algorithm, on both uniprocessor and multiprocessor scheduling. The key to k2U is a k-point effective schedulability test, which can be viewed as a "blackbox" interface. For any task model, if a corresponding k-point effective schedulability test can be constructed, then a sufficient utilization-based test can be automatically derived. We show the generality of k2U by applying it to different task models, which results in new and improved tests compared to the state-of-the-art. Analogously, a similar concept by testing only k points with a different formulation has been studied by us in another framework, called k2Q, which provides quadratic bounds or utilization bounds based on a different formulation of schedulability test. With the quadratic and hyperbolic forms, k2Q and k2U frameworks can be used to provide many quantitive features to be measured, like the total utilization bounds, speed-up factors, etc., not only for uniprocessor scheduling but also for multiprocessor scheduling. These frameworks can be viewed as a "blackbox" interface for schedulability tests and response-time analysis

Network Service Customization: End-Point Perspective (Proposal)

An important problem with cell-switched technologies such as Asynchronous Transfer Mode (ATM) is the provision of customized multiplexing behavior to applications. This customization takes the form of setting up processes in the network and end-points to meet application Quality of Service (QoS) requirements. The proposed thesis work examines the necessary components of a software architecture to provide QoS in the end-points of a cell-switched network. An architecture has been developed, and the thesis work will refine it using a driving application of the full-feedback teleoperation of a robotics system. Preliminary experimental results indicate that such teleoperation is possible using general-purpose workstations and a lightly-loaded ATM link. An important result of the experimental portion of the thesis work will be a study of the domain of applicability for various resource management techniques

Resources in process algebra

The Algebra of Communicating Shared Resources (ACSR) is a timed process algebra which extends classical process algebras with the notion of a resource. It takes the view that the timing behavior of a real-time system depends not only on delays due to process synchronization, but also on the availability of shared resources. Thus, ACSR employs resources as a basic primitive and it represents a real-time system as a collection of concurrent processes which may communicate with each other by means of instantaneous events and compete for the usage of shared resources. Resources are used to model physical devices such as processors, memory modules, communication links, or any other reusable resource of limited capacity. Additionally, they provide a convenient abstraction mechanism for capturing a variety of aspects of system behavior. In this paper we give an overview of ACSR and its probabilistic extension, PACSR, where resources can fail with associated failure probabilities. We present associated analysis techniques for performing qualitative analysis (such as schedulability analysis) and quantitative analysis (such as resource utilization analysis) of process-algebraic descriptions. We also discuss mappings between probabilistic and non-probabilistic models, which allow us to use analysis techniques from one algebra on models from the other