Scheduling Induced Bounds and the Verification of Preemptive Real-Time Systems

Distributed real-time and embedded (DRE) systems have stringent constraints on timeliness and other properties whose assurance is crucial to correct system behavior. Our previous research has shown that detailed models of essential middleware mechanisms can be developed, composed, and for constrained examples verified tractably, using state of the art timed automata model checkers. However, to apply model checking to a wider range of real-time systems, particularly those involving more general forms of preemptive concurrency, new techniques are needed to address decidability and tractability concerns. This paper makes three contributions to research on formal verification and validation of DRE systems. First, it describes how bounded fair scheduling policies introduce a quasi-cyclic structure in the state space of multi-threaded real-time systems. Second, it shows that bounds on the divergence of threads\u27 execution can be determined for that quasi-cyclic structure, which then can be exploited to reduce the complexity of model checking. Third, it presents a case study involving progress-based fair scheduling of multi-threaded processing pipelines, with which the approach is evaluated

The delay composition theorem on pipeline systems with non-preemptive priority varying scheduling algorithms

The delay composition theorem, by taking into account the fact that pipeline systems allow concurrent execution, expresses the upper-bounded delay of a real-time task as the sum of two summations, where the first one is linear to the number of stages of the system, and the second one is linear to the number of tasks running on the system. The schedulability analysis based on delay composition theorem performs better than traditional analysis techniques. In this paper we break one assumption that has been hold by previous works on delay composition theorem, namely each task has the same relative priority across all stages. We extend the theorem to pipeline systems running non-preemptive scheduling algorithm which may assign different relative priorities to a task on different stages

On static execution-time analysis

Proving timeliness is an integral part of the verification of safety-critical real-time systems. To this end, timing analysis computes upper bounds on the execution times of programs that execute on a given hardware platform. Modern hardware platforms commonly exhibit counter-intuitive timing behaviour: a locally slower execution can lead to a faster overall execution. Such behaviour challenges efficient timing analysis. In this work, we present and discuss a hardware design, the strictly in-order pipeline, that behaves monotonically w.r.t. the progress of a program's execution. Based on monotonicity, we prove the absence of the aforementioned counter-intuitive behaviour. At least since multi-core processors have emerged, timing analysis separates concerns by analysing different aspects of the system's timing behaviour individually. In this work, we validate the underlying assumption that a timing bound can be soundly composed from individual contributions. We show that even simple processors exhibit counter-intuitive behaviour - a locally slow execution can lead to an even slower overall execution - that impedes the soundness of the composition. We present the compositional base bound analysis that accounts for any such amplifying effects within its timing contribution. This enables a sound compositional analysis even for complex processors. Furthermore, we discuss hardware modifications that enable efficient compositional analyses.Echtzeitsysteme müssen unter allen Umständen beweisbar pünktlich arbeiten. Zum Beweis errechnet die Zeitanalyse obere Schranken der für die Ausführung von Programmen auf einer Hardware-Plattform benötigten Zeit. Moderne Hardware-Plattformen sind bekannt für unerwartetes Zeitverhalten bei dem eine lokale Verzögerung in einer global schnelleren Ausführung resultiert. Solches Zeitverhalten erschwert eine effiziente Analyse. Im Rahmen dieser Arbeit diskutieren wir das Design eines Prozessors mit eingeschränkter Fließbandverarbeitung (strictly in-order pipeline), der sich bzgl. des Fortschritts einer Programmausführung monoton verhält. Wir beweisen, dass Monotonie das oben genannte unerwartete Zeitverhalten verhindert. Spätestens seit dem Einsatz von Mehrkernprozessoren besteht die Zeitanalyse aus einzelnen Teilanalysen welche nur bestimmte Aspekte des Zeitverhaltens betrachten. Eine zentrale Annahme ist hierbei, dass sich die Teilergebnisse zu einer korrekten Zeitschranke zusammensetzen lassen. Im Rahmen dieser Arbeit zeigen wir, dass diese Annahme selbst für einfache Prozessoren ungültig ist, da eine lokale Verzögerung zu einer noch größeren globalen Verzögerung führen kann. Für bestehende Prozessoren entwickeln wir eine neuartige Teilanalyse, die solche verstärkenden Effekte berücksichtigt und somit eine korrekte Komposition von Teilergebnissen erlaubt. Für zukünftige Prozessoren beschreiben wir Modifikationen, die eine deutlich effizientere Zeitanalyse ermöglichen

Memory-processor co-scheduling in fixed priority systems

A major obstacle towards the adoption of multi-core platforms for real-time systems is given by the difficulties in characterizing the interference due to memory contention. The simple fact that multiple cores may simultaneously access shared memory and communication resources introduces a significant pessimism in the timing and schedulability analysis. To counter this problem, predictable execution models have been proposed splitting task executions into two consecutive phases: a memory phase in which the required instruction and data are pre-fetched to local memory (M-phase), and an execution phase in which the task is executed with no memory contention (C-phase). Decoupling memory and execution phases not only simplifies the timing analysis, but it also allows a more efficient (and predictable) pipelining of memory and execution phases through proper co-scheduling algorithms. In this paper, we take a further step towards the design of smart co-scheduling algorithms for sporadic real-time tasks complying with the M/C (memory-computation) model. We provide a theoretical framework that aims at tightly characterizing the schedulability improvement obtainable with the adopted M/C task model on a single-core systems. We identify a tight critical instant for M/C tasks scheduled with fixed priority, providing an exact response-time analysis with pseudo-polynomial complexity. We show in our experiments that a significant schedulability improvement may be obtained with respect to classic execution models, placing an important building block towards the design of more efficient partitioned multi-core systems

An Examination of the US Residential Heating Market

This paper outlines the US residential space heating market and highlights thirteen disruptive companies whose products decarbonize some link in the space heating supply chain. The goal of the paper is to provide Energy Impact Partners (EIP) with a strong understanding of market trends, regional switching costs, customer behaviors, and policy incentives. Additionally, we present an investment landscape of disruptive companies from which EIP may choose to pursue specific investment objectives. The US residential space heating market may be thought of as a mix of space heating fuel sources, such as natural gas and electricity, and a mix of space heating technologies, such as Furnaces and Heat Pumps. Four major trends stick out. First, Furnaces dominate the technology landscape as the most popular heating technology. Second, natural gas and electricity are the two main fuel types used for space heating, with 51% of households using natural gas and 37% of households using electricity. Third, the mixes of fuel and equipment have changed since 2001 largely due to higher population growth in southern regions where electricity and Heat Pumps provide space heating for most homes. Fourth, according to utility executives interviewed the mix of fuel and technology will not change drastically over the next ten years. Payback periods calculated are often long, greater than 10 years, making the switch to less carbon intensive fuel sources or less energy intensive technologies less appealing to the average homeowner. Furthermore, customer behavior hinders the switch to decarbonizing technologies because most individuals do not view space heating equipment as aspirational purchases and will only replace equipment upon failure – which often happens during the winter – forcing them to seek out the quickest fix rather than shop around for an alternative option, even if that option can save money through lower operating costs. Several federal and state incentives exist to motivate homeowners to decarbonize their space heating system. More details are provided in Chapter 7. Ultimately, the paper concludes with four insights for EIP with regards to investing in space heating startups. These insights revolve around the projected energy and technology mix, where innovation occurs in the space heating supply chain, customer behavior in purchasing decisions, and the importance of government policy for a startup’s success.Master of ScienceSchool for Environment and SustainabilityUniversity of Michiganhttps://deepblue.lib.umich.edu/bitstream/2027.42/146738/1/An Examination of the US Residential Heating Market_338.pd

Extensible Energy Planning Framework for Preemptive Tasks

Cyber-physical systems (CSPs) are demanding energy-efficient design not only of hardware (HW), but also of software (SW). Dynamic Voltage and and Frequency Scaling (DVFS) and Dynamic Power Manage (DPM) are most popular techniques to improve the energy efficiency. However, contemporary complicated HW and SW designs requires more elaborate and sophisticated energy management and efficiency evaluation techniques. This paper is concerned about energy supply planning for real-time scheduling systems (units) of which tasks need to meet deadlines. This paper presents a modelbased compositional energy planning technique that computes a minimal ratio of processor frequency that preserves schedulability of independent and preemptive tasks. The minimal ratio of processor frequency can be used to plan the energy supply of real-time components. Our model-based technique is extensible by refining our model with additional features so that energy management techniques and their energy efficiency can be evaluated by model checking techniques. We exploit the compositional framework for hierarchical scheduling systems and provide a new resource model for the frequency computation. As results, our use-case for avionics software components shows that our new method outperforms the classical real-time calculus (RTC) method, requiring 36.21% less frequency ratio on average for scheduling units under RM than the RTC method

Environmental Regulation, Energy, and Market Entry

As my contribution to a symposium, I was asked to identify and to discuss conflicts between environmental regulation and pursuit of the goals of national energy policy. I identify three contexts in which I see clear conflicts between environmental regulation and energy policy - gasoline production, importation of liquefied natural gas, and transmission of electricity. In each case, I conclude that the conflict is attributable to state and local regulations. In the case of the gasoline market, I conclude that the market is beginning to perform poorly because of a combination of state land use regulations that make it impossible to construct new refineries and state gasoline-type mandates that are in the process of transforming the highly competitive and efficient national gasoline market into scores of much smaller inefficient markets that are increasingly susceptible to both unilateral and collusive exercises of market power. In the case of the natural gas market, I conclude that state and local government attempts to assert the power to veto federally approved liquefied natural gas terminals place us in jeopardy of experiencing a devastating shortage of natural gas in the next few years. In the case of electricity transmission, I conclude that our rapidly growing shortage of transmission capacity is already costing us many billions of dollars per year and increasing dramatically our vulnerability to widespread blackouts and price spikes, and that the shortage is attributable primarily to state and local land use regulation. In each case, the conflict can be eliminated only by reducing the power of state and local regulators and/or by transferring some regulatory power from state and local institutions to federal institutions