Analysis of Dynamic Memory Bandwidth Regulation in Multi-core Real-Time Systems

One of the primary sources of unpredictability in modern multi-core embedded systems is contention over shared memory resources, such as caches, interconnects, and DRAM. Despite significant achievements in the design and analysis of multi-core systems, there is a need for a theoretical framework that can be used to reason on the worst-case behavior of real-time workload when both processors and memory resources are subject to scheduling decisions. In this paper, we focus our attention on dynamic allocation of main memory bandwidth. In particular, we study how to determine the worst-case response time of tasks spanning through a sequence of time intervals, each with a different bandwidth-to-core assignment. We show that the response time computation can be reduced to a maximization problem over assignment of memory requests to different time intervals, and we provide an efficient way to solve such problem. As a case study, we then demonstrate how our proposed analysis can be used to improve the schedulability of Integrated Modular Avionics systems in the presence of memory-intensive workload.Comment: Accepted for publication in the IEEE Real-Time Systems Symposium (RTSS) 2018 conferenc

Study, analysis and new scheduling proposals in partitioned real-time systems

[ES] En nuestra vida cotidiana, cada vez más ordenadores controlan nuestro entorno: teléfonos móviles, procesos industriales, asistencia a la conducción, etc. Todos estos sistemas presentan requisitos estrictos para garantizar un comportamiento adecuado. En muchos de estos sistemas, cumplir con las restricciones de tiempo es un factor tan importante como el resultado lógico de los cálculos. Desde hace aproximadamente 40 años, los sistemas en tiempo real son muy atractivos en el campo de la computación y hoy en día se aplican en áreas de gran alcance como aplicaciones industriales, aplicaciones aeroespaciales, telecomunicaciones, electrónica de consumo, etc. Algunos retos a abordar en el campo del tiempo real son el determinismo y la predecibilidad del comportamiento temporal del sistema. En este sentido, garantizar la ejecución del programa y los tiempos de respuesta del sistema son requisitos esenciales que deben cumplirse estrictamente a través de estrategias apropiadas de planificación de tareas. Además, las arquitecturas multiprocesador se están volviendo más populares debido al hecho de que las capacidades de procesamiento y los recursos computacionales de los sistemas están aumentando. Un estudio reciente estima que existe una tendencia creciente entre las arquitecturas multiprocesador a combinar diferentes niveles de criticidad en el mismo sistema. En este sentido, proporcionar aislamiento entre las aplicaciones es extremadamente necesario. La tecnología particionada es capaz de lidiar con este propósito. Además, la gestión de la energía es un problema relevante en los sistemas en tiempo real. Muchos sistemas empotrados de tiempo real, como dispositivos portátiles o robots móviles que requieren baterías, buscan encontrar técnicas que reduzcan el consumo de energía y, como consecuencia, aumenten la vida útil de sus baterías. También se obtienen claros beneficios operativos, financieros, monetarios y ambientales al minimizar el consumo de energía. Con todo ello, este trabajo aborda el problema de planificabilidad y contribuye al estudio de las nuevas técnicas de planificación en sistemas particionados de tiempo real. Estas técnicas proporcionan el tiempo mínimo para planificar de manera factible conjuntos de tareas. Además, se proponen técnicas de asignación para sistemas multiprocesador cuyo objetivo principal es reducir el consumo de energía del sistema global. Finalmente, se presentan los resultados obtenidos así como los trabajos futuros relacionados con este trabajo[CA] En la nostra vida quotidiana, cada vegada més ordenadors controlen el nostre entorn: telèfons mòbils, processos industrials, assistència a la conducció, etc. Tots aquests sistemes presenten requisits estrictes per a garantir un comportament adequat. En molts d' aquests sistemes, complir amb les restriccions de temps és un factor tan important com el resultat lògic dels càlculs. Des de fa aproximadament 40 anys, els sistemes en temps real són molt atractius en el camp de la computació i hui dia s' apliquen en àrees de gran abast com a aplicacions industrials, aplicacions aeroespacials, telecomunicacions, electrònica de consum, etc. Alguns reptes a abordar en el camp del temps real són el determinisme i la predictibilitat del comportament temporal del sistema. En aquest sentit, garantir l'execució del programa i els temps de resposta del sistema són requisits essencials que han de complir-se estrictament a través d'estratègies apropiades de planificació de tasques. A més, les arquitectures multiprocessador s'estan tornant més populars a causa del fet que les capacitats de processament i els recursos computacionals dels sistemes estan augmentant. Un estudi recent estima que existeix una tendència creixent entre les arquitectures multiprocessador a combinar diferents nivells de criticitat en el mateix sistema. En aquest sentit, proporcionar aïllament entre les aplicacions és extremadament necessari. La tecnologia particionada és capaç de bregar amb aquest propòsit. A més, la gestió de l'energia és un problema rellevant en els sistemes en temps real. Molts sistemes embebits de temps real, com a dispositius portàtils o robots mòbils que requereixen bateries, busquen trobar tècniques que reduïsquen el consum d'energia i, com a conseqüència, augmenten la vida útil de les seues bateries. També s'obtenen clars beneficis operatius, financers, monetaris i ambientals en minimitzar el consum d'energia. Amb tot això, aquest treball aborda el problema de planificabilitat i contribueix a l'estudi de les noves tècniques de planificació en sistemes particionats de temps real. Aquestes tècniques proporcionen el temps mínim per a planificar de manera factible conjunts de tasques. A més, es proposen tècniques d'assignació per a sistemes multiprocessador l'objectiu principal del qual és reduir el consum d'energia del sistema global. Finalment, es presenten els resultats obtinguts així com els treballs futurs relacionats amb aquest treball.[EN] In our everyday lives, more and more computers are controlling our environment: mobile phones, industrial processes, driving assistance, etc. All these systems present strict requirements to ensure proper behaviour. In many of these systems, the time at which the action is delivered is as important as the logical result of the computation. About 40 years ago, real-time systems began to attract attention in computing field and nowadays are applied in wide ranging areas as industrial applications, aerospace, telecommunication applications, consumer electronics, etc. Some real-time challenges that must be addressed are determinism and predictability of the temporal behaviour of the system. In this sense, to guarantee program execution and system response times are essential requirements that must be strictly met through appropriate task scheduling strategies. Furthermore, multiprocessor architectures are becoming more popular due to the fact that processing capabilities and computational resources are increasing. A recent study estimates that there is an increasing tendency among multiprocessor architectures to combine different levels of criticality in the same system. In this sense, to provide isolation between applications is extremely required. Partitioned technology is able to deal with this purpose. In addition, energy management is a relevant problem in real-time systems. Many real-time embedded systems, as wearable devices or mobile robots that require batteries, seek to find techniques that reduce the energy consumption and, as a consequence, increase the lifetime of their batteries. Also clear operational, financial, monetary and environmental gains are reached when minimizing energy consumption. Faced with all this, this work addresses the problem of schedulability and contributes to the study of new scheduling techniques in partitioned real-time systems. These techniques provide the minimum time to feasible schedule tasks sets. Moreover, allocation techniques for multicore systems whose main objective is to reduce the energy consumption of the overall system are also proposed. Finally, some of the obtained results are discussed as conclusions and future works are introduced.Guasque Ortega, A. (2019). Study, analysis and new scheduling proposals in partitioned real-time systems [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/135279TESI

A survey of techniques for reducing interference in real-time applications on multicore platforms

This survey reviews the scientific literature on techniques for reducing interference in real-time multicore systems, focusing on the approaches proposed between 2015 and 2020. It also presents proposals that use interference reduction techniques without considering the predictability issue. The survey highlights interference sources and categorizes proposals from the perspective of the shared resource. It covers techniques for reducing contentions in main memory, cache memory, a memory bus, and the integration of interference effects into schedulability analysis. Every section contains an overview of each proposal and an assessment of its advantages and disadvantages.This work was supported in part by the Comunidad de Madrid Government "Nuevas Técnicas de Desarrollo de Software de Tiempo Real Embarcado Para Plataformas. MPSoC de Próxima Generación" under Grant IND2019/TIC-17261

Heterogeneous models and analyses in the design of real-time embedded systems - an avionic case-study

The development of embedded systems according to Model-Driven Development relies on two complementary activities: system mod- eling on the one hand and analysis of the non-functional properties, such as timing properties, on the other hand. Yet, the coupling be- tween models and analyses remains largely disregarded so far: e.g. how to apply an analysis on a model? How to manage the analysis process? This paper presents an application of our research on this topic. In particular, we show that our approach makes it possible to combine heterogeneous models and analyses in the design of an avionic system. We use two languages to model the system at di erent levels of abstraction: the industry standard AADL (Ar- chitecture Analysis and Design Language) and the more recent implementation-oriented CPAL language (Cyber-Physical Action Language). We then combine di erent real-time scheduling analy- ses so as to gradually de ne the task and network parameters and nally validate the schedulability of all activities of the system

Exploring Alternatives to use Master/Slave Full Duplex Switched Ethernet for Avionics Embedded Applications

The complexity of distributed real-time systems, including military embedded applications, is increasing due to an increasing number of nodes, their functionality and higher amounts of exchanged data. This higher complexity imposes major development challenges when nonfunctional properties must be enforced. On the other hand, the current military communication networks are a generation old and are no longer effective in facing such increasingly complex requirements. A new communication network, based on Full Duplex Switched Ethernet and Master/slave approach, has been proposed previously. However, this initial approach is not efficient in terms of network bandwidth utilization. In this paper we propose two new alternative approaches that can use the network bandwidth more efficiently. In addition we provide a preliminary qualitative assessment of the three approaches concerning different factors such as performance, scalability, complexity and flexibility

Combined Security and Schedulability Analysis for MILS Real-Time Critical Architectures

Real-time critical systems have to comply with stringent timing constraints, otherwise, disastrous consequences can occur at runtime. A large effort has been made to propose models and tools to verify timing constraints by schedulability analysis at the early stages of system designs. Fewer efforts have been made on verifying the security properties in these systems despite the fact that sinister consequences can also happen if these properties are compromised. In this article, we investigate how to jointly verify security and timing constraints. We show how to model a security architecture (MILS) and how to verify both timing constraints and security properties. Schedulability is investigated by the mean of scheduling analysis methods implemented into the Cheddar scheduling analyzer. Experiments are conducted to show the impact that improving security has on the schedulability analysis