On schedulability and time composability of data aggregation networks (original) (raw)
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Critical embedded systems are often designed as a set of real-time tasks, running on shared computing modules, and communicating through networks. Because of their critical nature, such systems have to meet strict timing properties. To help the designers to prove the correctness of their system, the real-time systems community has developed numerous approaches for analysing the worst case scenarios either on the processors (e.g., worst case response time of a task) or on the networks (e.g., worst case traversal time of a message). These approaches provide results only for local components behaviours. However, there is a growing need for having a global view of the system, in order to determine end-to-end properties. Such a property applies to functional chains which describe the behaviour of sequences of tasks. We propose an approach to analyse worst case behaviour along functional chains in critical embedded systems. It is based on mixed integer linear programming (MILP) and is general in the sense that it can be applied to a variety of end-to-end properties. This paper focuses on two essential properties: end-to-end latency and temporal consistency.
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W e address the issue of guaranteeing applicationto-application deadlines of messages in distributed real-time systems. Most of the previous studies have focused on either host subsystem or network subsystem. Our study considers the entire integrated system. W e develop two methods to test whether the message deadlines are met. The first method, called the independent method, obtains conservative estimates of message delays b y independently analyzing each subsystem. This method is easy to use and eficient, but may sometimes give pessimistic results. The second method, called the integrated method, computes the delays more accurately b y modeling interactions among the subsystems in greater detail. Performance of the two methods is evaluated in terms of the p robability of guaranteeing message sets for given host utilization.
Issues in schedulability analysis of real-time systems
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Due to the critical nature o f r eal-time systems, there is an ever growing burden on the designer to not only guarantee that the tasks would meet their deadlines at design time, but would continue to do so as the system evolves. This implies that the schedulability analysis has to be r obust. In this study we identify the sensitivity of schedulability analysis to the task execution times. The impact, this parameter has on the schedulability analysis is captured by formulating a general scaling problem. This problem is shown to relate to the problems of scalability, portability and execution time estimation. A technique to solve this general problem is developed. A proof of correctness and optimality of the technique is presented.
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We investigate into the validity of the rate monotonic analysis techniques for distributed hard real time systems. A recent paper has shown that the algorithm developed by K. Tindell and J. Clark (1994) for the analysis of this kind of system was incomplete because it did not test all the possible cases. We prove that the algorithm is valid as it is stated and that it effectively obtains an upper bound for the worst case response times to external events in distributed systems, since the longest response always occurs within the cases that are currently tested by this algorithm. In addition, we extend the analysis technique to determine an upper bound for the local response times of particular actions in a response to an event, thus allowing the definition and verification of local deadlines for elementary actions in distributed systems
ACM SIGBED Review, 2012
Often, component-based real-time systems are modeled with trigger and data chains. The end-to-end timing requirements on trigger chains are different from those on data chains. For a trigger chain, the interest lies in the calculation of holistic response time and its comparison with end-to-end deadline. Whereas, the schedulability of a data chain requires a comparison between its end-to-end latencies and corresponding deadlines. We discuss the problem of translating end-to-end timing requirements unambiguously from component-based real-time systems into timing analysis models which are required as input by the analysis tools. We also provide preliminary guidelines for such translations in the existing industrial tool suite.
Schedulability Analysis of the Arbitrated Real-Time Protocol (AR-TP)
2006
This presentation was held at the 14th International Workshop on Parallel and Distributed Real-Time Systems (WPDRTS 2006), a satellite workshop of IEEE 20th International Parallel & Distributed Processing Symposium (IPDPS 2006), April 25–29, 2006. Rhodes Island, Greece. It was made by Santiago Urueña Pascual, PhD Student working at the real-time research group (Sistemas de Tiempo Real y Arquitectura de Servicios Telemáticos, STRAST) of the UPM, Spain (Spanish: Universidad Politécnica de Madrid, Technical University of Madrid). Our research group is mainly working on hard real-time and embedded systems, especially critical ones. This was a 20 min. presentation, held at 15:30h, at the general session called “Real-Time Communication II”, session chaired by Giuseppe Lipari.