Resource-aware scheduling for 2D/3D multi-/many-core processor-memory systems

This dissertation addresses the complexities of 2D/3D multi-/many-core processor-memory systems, focusing on two key areas: enhancing timing predictability in real-time multi-core processors and optimizing performance within thermal constraints. The integration of an increasing number of transistors into compact chip designs, while boosting computational capacity, presents challenges in resource contention and thermal management. The first part of the thesis improves timing predictability. We enhance shared cache interference analysis for set-associative caches, advancing the calculation of Worst-Case Execution Time (WCET). This development enables accurate assessment of cache interference and the effectiveness of partitioned schedulers in real-world scenarios. We introduce TCPS, a novel task and cache-aware partitioned scheduler that optimizes cache partitioning based on task-specific WCET sensitivity, leading to improved schedulability and predictability. Our research explores various cache and scheduling configurations, providing insights into their performance trade-offs. The second part focuses on thermal management in 2D/3D many-core systems. Recognizing the limitations of Dynamic Voltage and Frequency Scaling (DVFS) in S-NUCA many-core processors, we propose synchronous thread migrations as a thermal management strategy. This approach culminates in the HotPotato scheduler, which balances performance and thermal safety. We also introduce 3D-TTP, a transient temperature-aware power budgeting strategy for 3D-stacked systems, reducing the need for Dynamic Thermal Management (DTM) activation. Finally, we present 3QUTM, a novel method for 3D-stacked systems that combines core DVFS and memory bank Low Power Modes with a learning algorithm, optimizing response times within thermal limits. This research contributes significantly to enhancing performance and thermal management in advanced processor-memory systems

Integrating security into real-time cyber-physical systems

Cyber-physical systems (CPS) such as automobiles, power plants, avionics systems, unmanned vehicles, medical devices, manufacturing and home automation systems have distinct cyber and physical components that must work cohesively with each other to ensure correct operation. Many cyber-physical applications have “real-time” constraints, i.e., they must function correctly within predetermined time scales. A failure to protect these systems could result in significant harm to humans, the system or even the environment. While traditionally such systems were isolated from external accesses and used proprietary components and protocols, modern CPS use off-the-shelf components and are increasingly interconnected, often via networks such as the Internet. As a result, they are exposed to additional attack surfaces and have become increasingly vulnerable to cyber attacks. Enhancing security for real-time CPS, however, is not an easy task due to limited resource availability (e.g., processing power, memory, storage, energy) and stringent timing/safety requirements. Security monitoring techniques for cyber-physical platforms (a) must execute with existing real-time tasks, (b) operate without impacting the timing and safety constraints of the control logic and (c) have to be designed and executed in a way that an adversary cannot easily evade it. The objective of my research is to increase security posture of embedded real-time CPS by integrating monitoring/detection techniques that defeat cyber attacks without violating timing/safety constraints of existing tasks. My dissertation work explores the real-time security domain and shows that by employing a combination of multiple scheduling/analysis techniques and interactions between hardware/software-based security extensions, it becomes feasible to integrate security monitoring mechanisms in real-time CPS without compromising timing/safety requirements of existing tasks. In this research, I (a) develop techniques to raise the responsiveness of security monitoring tasks by increasing their frequency of execution, (b) design a hardware-supported framework to prevent falsification of actuation commands — i.e., commands that control the state of the physical system and (c) propose metrics to trade-off security with real-time guarantees. The solutions presented in this dissertation require minimal changes to system components/parameters and thus compatible for legacy systems. My proposed frameworks and results are evaluated through both, simulations and experiments on real off-the-shelf cyber-physical platforms. The development of analysis techniques and design frameworks proposed in this dissertation will inherently make such systems more secure and hence, safer. I believe my dissertation work will bring researchers and system engineers one step closer to understand how to integrate two seemingly diverse yet important fields — real-time CPS and cyber-security — while gaining a better understanding of both areas

A Survey of Probabilistic Timing Analysis Techniques for Real-Time Systems

This survey covers probabilistic timing analysis techniques for real-time systems. It reviews and critiques the key results in the field from its origins in 2000 to the latest research published up to the end of August 2018. The survey provides a taxonomy of the different methods used, and a classification of existing research. A detailed review is provided covering the main subject areas: static probabilistic timing analysis, measurement-based probabilistic timing analysis, and hybrid methods. In addition, research on supporting mechanisms and techniques, case studies, and evaluations is also reviewed. The survey concludes by identifying open issues, key challenges and possible directions for future research

Computer Aided Verification

The open access two-volume set LNCS 11561 and 11562 constitutes the refereed proceedings of the 31st International Conference on Computer Aided Verification, CAV 2019, held in New York City, USA, in July 2019. The 52 full papers presented together with 13 tool papers and 2 case studies, were carefully reviewed and selected from 258 submissions. The papers were organized in the following topical sections: Part I: automata and timed systems; security and hyperproperties; synthesis; model checking; cyber-physical systems and machine learning; probabilistic systems, runtime techniques; dynamical, hybrid, and reactive systems; Part II: logics, decision procedures; and solvers; numerical programs; verification; distributed systems and networks; verification and invariants; and concurrency

Contributions to the safe execution of dynamic component-based real-time systems

Traditionally, real-time systems have based their design and execution on barely dynamic models to ensure, since design time, the temporal guarantees in the execution of their functionality. Great effort is being applied nowadays to progressively develop more dynamic systems, with the target of changing during their execution and to adapt themselves to their environment. The capability to change and to reconfigure themselves represents remarkable advantages as the capability to fix errors and to add new functionality with on-line updates. This means to be able to be updated without needing to stop the service, that may imply monetary losses in many cases. Design and development techniques based on components have become popular due to the use of components, which allows simplifying the system design, code reusability and updates through the substitution of components. The target of this thesis work is to provide certain degree of dynamism to real-time systems allowing them to replace components, incorporating new functionality of fixing existing bugs. On that purpose, a component-based framework is proposed, as well as the corresponding task in charge of providing dynamism to the system. The main contribution is to provide a framework to allow safe component replacements. Safe meaning that incorrect executions of tasks are avoided even y multiple tasks are executing concurrently and making use of the same data. Also that temporal guarantees are provided for every task. This framework incorporates a generic component model with real-time threads, a components replacement model with execution times that are known and bounded, and different strategies to apply such component replacement model. Some mechanisms to maintain a seamless and safe execution, regarding concurrency, before, during, and after applying the processes in charge of replacing running components are also described. Seamless execution means that components themselves do not perform the replacements, and safe means that temporal guarantees are provided and components are not affected in their execution. Part of these mechanisms are the system schedulability analysis and the framework tasks as well as reserving the needed resources for such scheduling to be correct. ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Los sistemas de tiempo real han basado tradicionalmente su desarrollo en modelos altamente predecibles ya que estos requieren garantías temporales en su ejecución. A lo largo de los años, la technología de tiempo real ha ido penetrando en diferentes campos de aplicación y ajustándose a paradigmas de desarrollo software más novedosos. Esto ha presentado y presenta en la actualidad un tremendo reto ya que estas aplicaciones suelen tener un alto grado de dinamismo, lo que entra en conflicto con la predictibilidad temporal y, en general la ejecución segura de los mismos. Hoy en dia se esta realizando un gran esfuerzo en el desarrollo de sistemas cada vez más dinamicos que permitan adaptar su estructura en tiempo de ejecución para adaptarse a entornos que presentan condiciones cambiantes. La capacidad de soportar este tipo de dinamismo presenta ventajas descatables como permitir corregir fallos y anadir funcionalidad mediante actualizaciones en caliente, es decir, poder actualizarse sin necesidad de realizar paradas en su servicio, lo que podria implicar costes monetarios en muchos casos o perdidas temporales de servicio. Por otro lado, las técnicas de diseño y desarrollo basadas en componentes se han hecho muy populares y su aplicación a los sistemas de tiempo real gana terreno día a día. Uno de los principales motivos de ellos es que el uso de componentes permite simplificar el diseño del sistema, la reutilizacion de codigo e incluso la actualizacion del mismo mediante la substitucion de componentes. En esta tesis se aborda el objetivo de proveer a los sistemas de tiempo real de cierto grado de dinamismo para poder reemplazar componentes de forma segura, que permita incorporar nuevas funcionalidades o corregir errores existentes. Para ello, en esta tesis se ha elaborado de un marco de trabajo para dar soporte a reemplazos de componentes de forma segura, entendiendo como tal que el hecho de que no se produzcan ejecuciones incorrectas debido a la ejecución concurrente de multiples tareas, asi como el garantizar los tiempos de ejecucion de cada tarea y acotar la duración temporal de los reemplazos. El marco de trabajo propuesto está basado, pues, en componentes de tiempo real, que tiene en cuenta los requisitos temporales en la ejecución de los componentes del sistema y de las tareas propias del marco que dan soporte a estos mecanismos de reemplazo. Este marco de trabajo incorpora un modelo generico de componente con tareas de tiempo real, un modelo de reemplazo de componentes cuyos tiempos de ejecucion son conocidos y limitados en tiempo y diferentes estrategias de aplicacion de dicho modelo de reemplazo de componente. Las contribuciones propuestas integran el analisis de la planificabilidad de los componentes del sistema y de las tareas del marco de componentes para permitir establecer los parámetros de reserva de los recursos necesarios para las tareas del marco. Por último, se realiza una validación empírica en la que se comprueba experimentalmente la validez del modelo tanto de forma genérica como en un escenario específico y determinando también los recursos necesarios para su implementación

Computer Aided Verification

The open access two-volume set LNCS 11561 and 11562 constitutes the refereed proceedings of the 31st International Conference on Computer Aided Verification, CAV 2019, held in New York City, USA, in July 2019. The 52 full papers presented together with 13 tool papers and 2 case studies, were carefully reviewed and selected from 258 submissions. The papers were organized in the following topical sections: Part I: automata and timed systems; security and hyperproperties; synthesis; model checking; cyber-physical systems and machine learning; probabilistic systems, runtime techniques; dynamical, hybrid, and reactive systems; Part II: logics, decision procedures; and solvers; numerical programs; verification; distributed systems and networks; verification and invariants; and concurrency

Flexible Scheduling in Middleware for Distributed rate-based real-time applications - Doctoral Dissertation, May 2002

Distributed rate-based real-time systems, such as process control and avionics mission computing systems, have traditionally been scheduled statically. Static scheduling provides assurance of schedulability prior to run-time overhead. However, static scheduling is brittle in the face of unanticipated overload, and treats invocation-to-invocation variations in resource requirements inflexibly. As a consequence, processing resources are often under-utilized in the average case, and the resulting systems are hard to adapt to meet new real-time processing requirements. Dynamic scheduling offers relief from the limitations of static scheduling. However, dynamic scheduling offers relief from the limitations of static scheduling. However, dynamic scheduling often has a high run-time cost because certain decisions are enforced on-line. Furthermore, under conditions of overload tasks can be scheduled dynamically that may never be dispatched, or that upon dispatch would miss their deadlines. We review the implications of these factors on rate-based distributed systems, and posits the necessity to combine static and dynamic approaches to exploit the strengths and compensate for the weakness of either approach in isolation. We present a general hybrid approach to real-time scheduling and dispatching in middleware, that can employ both static and dynamic components. This approach provides (1) feasibility assurance for the most critical tasks, (2) the ability to extend this assurance incrementally to operations in successively lower criticality equivalence classes, (3) the ability to trade off bounds on feasible utilization and dispatching over-head in cases where, for example, execution jitter is a factor or rates are not harmonically related, and (4) overall flexibility to make more optimal use of scarce computing resources and to enforce a wider range of application-specified execution requirements. This approach also meets additional constraints of an increasingly important class of rate-based systems, those with requirements for robust management of real-time performance in the face of rapidly and widely changing operating conditions. To support these requirements, we present a middleware framework that implements the hybrid scheduling and dispatching approach described above, and also provides support for (1) adaptive re-scheduling of operations at run-time and (2) reflective alternation among several scheduling strategies to improve real-time performance in the face of changing operating conditions. Adaptive re-scheduling must be performed whenever operating conditions exceed the ability of the scheduling and dispatching infrastructure to meet the critical real-time requirements of the system under the currently specified rates and execution times of operations. Adaptive re-scheduling relies on the ability to change the rates of execution of at least some operations, and may occur under the control of a higher-level middleware resource manager. Different rates of execution may be specified under different operating conditions, and the number of such possible combinations may be arbitrarily large. Furthermore, adaptive rescheduling may in turn require notification of rate-sensitive application components. It is therefore desirable to handle variations in operating conditions entirely within the scheduling and dispatching infrastructure when possible. A rate-based distributed real-time application, or a higher-level resource manager, could thus fall back on adaptive re-scheduling only when it cannot achieve acceptable real-time performance through self-adaptation. Reflective alternation among scheduling heuristics offers a way to tune real-time performance internally, and we offer foundational support for this approach. In particular, run-time observable information such as that provided by our metrics-feedback framework makes it possible to detect that a given current scheduling heuristic is underperforming the level of service another could provide. Furthermore we present empirical results for our framework in a realistic avionics mission computing environment. This forms the basis for guided adaption. This dissertation makes five contributions in support of flexible and adaptive scheduling and dispatching in middleware. First, we provide a middle scheduling framework that supports arbitrary and fine-grained composition of static/dynamic scheduling, to assure critical timeliness constraints while improving noncritical performance under a range of conditions. Second, we provide a flexible dispatching infrastructure framework composed of fine-grained primitives, and describe how appropriate configurations can be generated automatically based on the output of the scheduling framework. Third, we describe algorithms to reduce the overhead and duration of adaptive rescheduling, based on sorting for rate selection and priority assignment. Fourth, we provide timely and efficient performance information through an optimized metrics-feedback framework, to support higher-level reflection and adaptation decisions. Fifth, we present the results of empirical studies to quantify and evaluate the performance of alternative canonical scheduling heuristics, across a range of load and load jitter conditions. These studies were conducted within an avionics mission computing applications framework running on realistic middleware and embedded hardware. The results obtained from these studies (1) demonstrate the potential benefits of reflective alternation among distinct scheduling heuristics at run-time, and (2) suggest performance factors of interest for future work on adaptive control policies and mechanisms using this framework

A Survey of Probabilistic Schedulability Analysis Techniques for Real-Time Systems

This survey covers schedulability analysis techniques for probabilistic real-time systems. It reviews the key results in the field from its origins in the late 1980s to the latest research published up to the end of August 2018. The survey outlines fundamental concepts and highlights key issues. It provides a taxonomy of the different methods used, and a classification of existing research. A detailed review is provided covering the main subject areas as well as research on supporting techniques. The survey concludes by identifying open issues, key challenges and possible directions for future research

Scheduling and locking in multiprocessor real-time operating systems

With the widespread adoption of multicore architectures, multiprocessors are now a standard deployment platform for (soft) real-time applications. This dissertation addresses two questions fundamental to the design of multicore-ready real-time operating systems: (1) Which scheduling policies offer the greatest flexibility in satisfying temporal constraints; and (2) which locking algorithms should be used to avoid unpredictable delays? With regard to Question 1, LITMUSRT, a real-time extension of the Linux kernel, is presented and its design is discussed in detail. Notably, LITMUSRT implements link-based scheduling, a novel approach to controlling blocking due to non-preemptive sections. Each implemented scheduler (22 configurations in total) is evaluated under consideration of overheads on a 24-core Intel Xeon platform. The experiments show that partitioned earliest-deadline first (EDF) scheduling is generally preferable in a hard real-time setting, whereas global and clustered EDF scheduling are effective in a soft real-time setting. With regard to Question 2, real-time locking protocols are required to ensure that the maximum delay due to priority inversion can be bounded a priori. Several spinlock- and semaphore-based multiprocessor real-time locking protocols for mutual exclusion (mutex), reader-writer (RW) exclusion, and k-exclusion are proposed and analyzed. A new category of RW locks suited to worst-case analysis, termed phase-fair locks, is proposed and three efficient phase-fair spinlock implementations are provided (one with few atomic operations, one with low space requirements, and one with constant RMR complexity). Maximum priority-inversion blocking is proposed as a natural complexity measure for semaphore protocols. It is shown that there are two classes of schedulability analysis, namely suspension-oblivious and suspension-aware analysis, that yield two different lower bounds on blocking. Five asymptotically optimal locking protocols are designed and analyzed: a family of mutex, RW, and k-exclusion protocols for global, partitioned, and clustered scheduling that are asymptotically optimal in the suspension-oblivious case, and a mutex protocol for partitioned scheduling that is asymptotically optimal in the suspension-aware case. A LITMUSRT-based empirical evaluation is presented that shows these protocols to be practical

Embedded System Design

A unique feature of this open access textbook is to provide a comprehensive introduction to the fundamental knowledge in embedded systems, with applications in cyber-physical systems and the Internet of things. It starts with an introduction to the field and a survey of specification models and languages for embedded and cyber-physical systems. It provides a brief overview of hardware devices used for such systems and presents the essentials of system software for embedded systems, including real-time operating systems. The author also discusses evaluation and validation techniques for embedded systems and provides an overview of techniques for mapping applications to execution platforms, including multi-core platforms. Embedded systems have to operate under tight constraints and, hence, the book also contains a selected set of optimization techniques, including software optimization techniques. The book closes with a brief survey on testing. This fourth edition has been updated and revised to reflect new trends and technologies, such as the importance of cyber-physical systems (CPS) and the Internet of things (IoT), the evolution of single-core processors to multi-core processors, and the increased importance of energy efficiency and thermal issues