Real-time Scheduling Theory Research Articles

Partitioning real-time workloads on multi-core virtual machines

Modern real-time virtual machines and containers are starting to make it possible to support the execution of real-time applications in virtualized environments. Real-time scheduling theory already provides techniques for analyzing the schedulability of real-time applications executed in virtual machines, but most of the previous work focused on global scheduling while, excluding a few exceptions, the problem of partitioning real-time workloads on multi-core VMs has not been properly investigated yet. This paper discusses and presents a set of partitioning algorithms, based on both mathematical optimization and some heuristics, to tackle the problem of online admission control and partitioning. An experimental evaluation shows that some of the heuristic algorithms can be effectively used in practical settings, being capable to partition complex task sets in short times and introducing an allocation overhead near to the optimum one.

SET-MRTS: An empirical experiment tool for real-time scheduling and synchronization

In the real-time scheduling theory, schedulability and synchronization analyses are used to evaluate scheduling algorithms and real-time locking protocols, respectively, and the empirical synthesis experiment is one of the major methods to compare the performance of such analyses. However, since many sophisticated techniques have been adopted to improve the analytical accuracy, the implementation of such analyses and experiments is often time-consuming. This paper proposes a schedulability experiment toolkit for multiprocessor real-time systems (SET-MRTS), which provides a framework with infrastructures to implement the schedulability and synchronization analyses and the deployment of empirical synthesis experiments. Besides, with well-designed peripheral components for the input and output, experiments can be conducted easily and flexibly on SET-MRTS. This demonstration further proves the effectiveness of SET-MRTS in both functionality and availability.

Beyond the limitations of real-time scheduling theory: a unified scheduling theory for the analysis of real-time systems

We investigate the mathematical properties of event bound functions as they are used in the worst-case response time analysis and utilization tests. We figure out the differences and similarities between the two approaches. Based on this analysis, we derive a more general form do describe events and event bounds. This new unified approach gives clear new insights in the investigation of real-time systems, simplifies the models and will support algebraic proofs in future work. In the end, we present a unified analysis which allows the algebraic definition of any scheduler. Introducing such functions to the real-time scheduling theory will lead two a more systematic way to integrate new concepts and applications to the theory. Last but not least, we show how the response time analysis in dynamic scheduling can be improved.

Schedulability Analysis for Timed Automata With Tasks

Research on modeling and analysis of real-time computing systems has been done in two areas, model checking and real-time scheduling theory. In model checking, an expressive modeling formalism such as timed automata (TA) is used to model complex systems, but the analysis is typically very expensive due to state-space explosion. In real-time scheduling theory, the analysis techniques are highly efficient, but the models are often restrictive. In this paper, we aim to exploit the possibility of applying efficient analysis techniques rooted in real-time scheduling theory to analysis of real-time task systems modeled by timed automata with tasks (TAT). More specifically, we develop efficient techniques to analyze the feasibility of TAT-based task models (i.e., whether all tasks can meet their deadlines on single-processor) using demand bound functions (DBF), a widely used workload abstraction in real-time scheduling theory. Our proposed analysis method has a pseudo-polynomial time complexity if the number of clocks used to model each task is bounded by a constant, which is much lower than the exponential complexity of the traditional model-checking based analysis approach (also assuming the number of clocks is bounded by a constant). We apply dynamic programming techniques to implement the DBF-based analysis framework, and propose state space pruning techniques to accelerate the analysis process. Experimental results show that our DBF-based method can analyze a TAT system with 50 tasks within a few minutes, which significantly outperforms the state-of-the-art TAT-based schedulability analysis tool TIMES.

Q-CSF: Quantum-Aware Compositional Scheduling Framework for Hierarchical Real-Time Systems

Component-based design has received considerable attention owing to its advantages in terms of security and safety when developing modern embedded systems. To effectively allocate computing resources to components in these systems, real-time component-based scheduling theory has been studied from various perspectives. The main advantage of component-based scheduling theory is that it guarantees the schedulability of an independent component and composability of multiple components. However, the existing component scheduling theory cannot be directly applied to real hardware platform due to an impractical assumption that resource allocation must be conducted across the continuum of real numbers, whereas actual operating systems (or virtualization systems) allocate resources in units of scheduling time quantum. In this study, we proposed a new efficient resource allocation and supply mechanism for quantumized hardware platforms while using real-number-based component interface. In simulation results with randomly-generated workloads, our approach reduced the overhead of existing approaches by up to 97.1% in an individual component. In composition of multiple components, our approach has up to 0.41 better acceptance ratio than existing approaches.

Utilization-Tensity Bound for Real-Time DAG Tasks under Global EDF Scheduling

Utilization bound is a well-known concept in real-time scheduling theory for sequential periodic tasks, which can be used both for quantifying the performance of scheduling algorithms and as efficient schedulability tests. However, the schedulability of parallel real time task graphs depends on not only utilization, but also another parameter tensity , the ratio between the longest path length and period. In this paper, we use utilization-tensity bounds to better characterize the schedulability of parallel real-time tasks. In particular, we derive utilization-tensity bounds for parallel DAG tasks under global EDF scheduling, which facilitate significantly more precise schedulability analysis than the state-of-the-art analysis techniques based on capacity augmentation bound and response time analysis. Moreover, we apply the above results to the federated scheduling paradigm to improve the system schedulability by choosing proper scheduling strategies for tasks with different workload and structure features.

Application validation on RTDroid

Android is becoming used more frequently in domains that expect some real-time guarantees. To facilitate the adoption of Android for programming real-time systems, this work presents a first effort to apply real-time scheduling theories to a real-time extension on Android, RTDroid. We integrate real-time properties specified in RT-Droid's application manifest with an existing real-time scheduling framework, Cheddar. We leverage Cheddar to perform schedulability analysis and feasibility tests, based on the properties of RTDroid application components specified in the application manifest. This paper details our integration process and reports our experience of validating real-time properties in a real-time application developed on RTDroid.

Uniprocessor scheduling of real-time synchronous dataflow tasks

The synchronous dataflow graph (SDFG) model is widely used today for modeling real-time applications in safety-critical application domains. Schedulability analysis techniques that are well understood within the real-time scheduling community are applied to the analysis of recurrent real-time workloads that are represented using this model. An enhancement to the standard SDFG model is proposed, which supports the specification of a real-time latency constraint between a specified input and a specified output of an SDFG. A polynomial-time algorithm is derived for representing the computational requirement of each such enhanced SDFG task in terms of the notion of the demand bound function (dbf), which is widely used in real-time scheduling theory for characterizing computational requirements of recurrent processes represented by, e.g., the sporadic task model. By so doing, the extensive dbf-centered machinery that has been developed in real-time scheduling theory for the hard-real-time schedulability analysis of systems of recurrent tasks may be applied to the analysis of systems represented using the SDFG model as well. The applicability of this approach is illustrated by applying prior results from real-time scheduling theory to construct an exact preemptive uniprocessor schedulability test for collections of independent recurrent processes that are each represented using the enhanced SDFG model.

Towards the systematic analysis of non-functional properties in Model-Based Engineering for real-time embedded systems

The real-time scheduling theory provides analytical methods to assess the temporal predictability of embedded systems. Nevertheless, their use is limited in a Model-Based Systems Engineering approach. In fact, the large number of applicability conditions makes the use of real-time scheduling analysis tedious and error-prone. Key issues are left to the engineers: when to apply a real-time scheduling analysis? What to do with the analysis results? This article presents an approach to systematize and then automate the analysis of non-functional properties in Model-Based Systems Engineering. First, preconditions and postconditions define the applicability of an analysis. In addition, contracts specify the analysis interfaces, thereby enabling to reason about the analysis process. We present a proof-of-concept implementation of our approach using a combination of constraint languages (REAL for run-time analysis) and specification languages (Alloy for describing interfaces and reasoning about them). This approach is experimented on architectural models written with the Architecture Analysis and Design Language (AADL).

Efficient Schedulability Test for Dynamic-Priority Scheduling of Mixed-Criticality Real-Time Systems

Systems in many safety-critical application domains are subject to certification requirements. In such a system, there are typically different applications providing functionalities that have varying degrees of criticality. Consequently, the certification requirements for functionalities at these different criticality levels are also varying, with very high levels of assurance required for a highly critical functionality, whereas relatively low levels of assurance are required for a less critical functionality. Considering the timing assurance given to various applications in the form of guaranteed budgets within deadlines, a theory of real-time scheduling for such multi-criticality systems has been recently under development. In particular, an algorithm called Earliest Deadline First with Virtual Deadlines (EDF-VD) has shown a lot of promise for systems with two criticality levels, especially in terms of practical performance demonstrated through experiment results. In this article, we design a new schedulability test for EDF-VD that extends these performance benefits to multi-criticality systems. We propose a new test based on demand bound functions and also present a novel virtual deadline assignment strategy. Through extensive experiments, we show that the proposed technique significantly outperforms existing strategies for a variety of generic real-time systems.

On the Improved Hard Real-Time Scheduling of Cyclo-Static Dataflow

Recently, it has been shown that the hard real-time scheduling theory can be applied to streaming applications modeled as acyclic Cyclo-Static Dataflow (CSDF) graphs. However, this recent approach is not always efficient in terms of throughput and processor utilization. Therefore, in this article, we propose an improved hard real-time scheduling approach to schedule streaming applications modeled as acyclic CSDF graphs on a Multiprocessor System-on-Chip (MPSoC) platform. The proposed approach converts each actor in a CSDF graph to a set of real-time periodic tasks. The conversion enables application of many hard real-time scheduling algorithms that offer fast calculation of the required number of processors for scheduling the tasks. In addition, we propose a method to reduce the graph latency when the converted tasks are scheduled as real-time periodic tasks. We evaluate the performance and time complexity of our approach in comparison to several existing scheduling approaches. Experiments on a set of real-life streaming applications demonstrate that our approach (1) results in systems with higher throughput and better processor utilization in comparison to the existing hard real-time scheduling approach for CSDF graphs, while requiring comparable time for the system derivation; (2) delivers shorter application latency by applying the proposed method for graph latency reduction while providing better throughput and processor utilization when compared to the existing hard real-time scheduling approach; (3) gives the same throughput as the existing periodic scheduling approach for CSDF graphs, but requires much shorter time to derive the task schedule and tasks’ parameters (periods, start times, and so on); and (4) gives the throughput that is equal to or very close to the maximum achievable throughput of an application obtained via self-timed scheduling, but requires much shorter time to derive the schedule. The total time needed for the proposed conversion approach and the calculation of the minimum number of processors needed to schedule the tasks and the calculation of the size of communication buffers between tasks is in the range of seconds.

Optimal Scheduling for Real-Time Jobs in Energy Harvesting Computing Systems

In this paper, we study a scheduling problem, in which every job is associated with a release time, deadline, required computation time, and required energy. We focus on an important special case where the jobs execute on a uniprocessor system that is supplied by a renewable energy source and use a rechargeable storage unit with limited capacity. Earliest deadline first (EDF) is a class one online algorithm in the classical real-time scheduling theory where energy constraints are not considered. We propose a semi-online EDF-based scheduling algorithm theoretically optimal (i.e., processing and energy costs neglected). This algorithm relies on the notions of energy demand and slack energy, which are different from the well known notions of processor demand and slack time. We provide an exact feasibility test. There are no restrictions on this new scheduler: each job can be one instance of a periodic, aperiodic, or sporadic task with deadline.

Composition of design patterns

This article deals with performance verification of architecture models of real-time embedded systems. We investigate scheduling analysis of multi-tasks applications running on real-time operating systems (RTOS in this article). Scheduling analysis on these types of system can be performed with the real-time scheduling theory, but applying it is a complicated task. To allow designer to automatically apply this theory, we propose several architectural design patterns. Each architectural design pattern models a classical task synchronization or communication protocol available in RTOSes. In this article, we focus on those design patterns composition. We show how to compose the proposed design patterns and how scheduling analysis can be run with them.

A Platform Independent Model for MPSoC Scheduling Using UML-RT

Integration of object modeling and real-time scheduling theory is a key to successful use of object technology for real-time software. Unified Modeling language (UML) is widely used modeling language in software engineering community which supports object-oriented design which in turn encourages component reuse. Recently, system modeling with a Unified Modeling language (UML) is an active research area for developing MPSoC real-time system. Our aim is to propose a unified modeling approach from model design, simulation, until code generation to analyze Rate Monotonic Algorithm for global, partitioned and semi- partitioned scheduling for MPSoC using UML-Real Time. As a technical contribution success ratio and average processor utilization for the generated periodic tasks is compared with various scheduling principles, to validate our proposal.

Applicability of real-time schedulability analysis on a software radio protocol

In this paper, we present our experience on integrating timing constraint verification and analysis, by using the real-time scheduling theory, in an industrial context. The verification process has been integrated into a design flow at THALES Communications & Security. We focus our work on Software Radio Protocols (SRP). We have used Model-Driven Engineering technologies and the Cheddar schedulability analysis tool for our experiment. We show how we have modeled a complete SRP in UML MARTE, a profile for real-time embedded systems, before using model transformation to extract information for schedulability analysis with Cheddar.

An Ada design pattern recognition tool for AADL performance analysis

This article deals with performance verification of architecture models of real-time embedded systems. Although real-time scheduling theory provides numerous analytical methods called feasibility tests for scheduling analysis, their use is a complicated task. In order to assist an architecture model designer in early verification, we provide an approach, based on real-time specific design patterns, enabling an automatic schedulability analysis. This analysis is based on existing feasibility tests, whose selection is deduced from the compliance of the system to a design pattern and other system's properties. Those conformity verifications are integrated into a schedulability tool called Cheddar. We show how to model the relationships between design patterns and feasibility tests and design patterns themselves. Based on these models, we apply a model-based engineering process to generate, in Ada, a feasibility test selection tool. The tool is able to detect from an architecture model which are the feasibility tests that the designer can apply. We explain a method for a designer willing to use this approach. We also describe the design patterns defined and the selection algorithm.

Architecture, mechanisms and scheduling analysis tool for multicore time- and space-partitioned systems

Time- and space-partitioned systems (TSP) are a current trend in aerospace. They are employed to integrate a heterogeneous set of functions (different criticalities, real-time requirements, and origins) in a shared computing platform, fulfilling individual partitions' and global real-time properties. Applications are separated into logical partitions, scheduled according to predefined partition scheduling tables (PSTs). In this paper we expose our current work on exploiting multiprocessor/multicore processor platforms to add capacity, flexibility and safety to the current state of the art in TSP systems. We propose architectural evolutions, as well as the development of a schedule analysis and generation tool based on Cheddar. The tool will incorporate and extend real-time scheduling theory results, and be able to analyse the feasibility of PSTs and aid the generation of PSTs from the individual timing requirements of each function.

PADS: An approach to modeling resource demand and supply for the formal analysis of hierarchical scheduling

As real-time embedded systems become more complex, resource partitioning is increasingly used to guarantee real-time performance. Recently, several compositional frameworks of resource partitioning have been proposed using real-time scheduling theory with various notions of real-time tasks running under restricted resource supply environments. However, these real-time scheduling-based approaches are limited in their expressiveness in that, although capable of describing resource-demand tasks, they are unable to model resource supply. This paper describes a process algebraic framework PADSfor reasoning about resource demand and resource supply inspired by the timed process algebra ACSR. In ACSR, real-time tasks are specified by enunciating their consumption needs for resources. To also accommodate resource-supply processes in PADS, given a resource c p u , we write c p u ¯ to denote the availability of c p u for a requesting task process. Using PADS, we define a supply-demand relation where a pair ( T , S ) belongs to the relation if the demand process T can be scheduled under supply S . We develop a theory of compositional schedulability analysis as well as a technique for synthesizing an optimal supply process for a set of tasks. Furthermore, we define ordering relations between supplies which describe when a supply offers more resource capacity than another. With this notion it is possible to formally represent hierarchical scheduling approaches that assign more “generous” resource allocations to tasks in exchange for a simple representation. We illustrate our techniques via a number of examples.

Power efficient rate monotonic scheduling for multi-core systems

More computational power is offered by current real-time systems to cope with CPU intensive applications. However, this facility comes at the price of more energy consumption and eventually higher heat dissipation. As a remedy, these issues are being encountered by adjusting the system speed on the fly so that application deadlines are respected and also, the overall system energy consumption is reduced. In addition, the current state of the art of multi-core technology opens further research opportunities for energy reduction through power efficient scheduling. However, the multi-core front is relatively unexplored from the perspective of task scheduling. To the best of our knowledge, very little is known as of yet to integrate power efficiency component into real-time scheduling theory that is tailored for multi-core platforms. In this paper, we first propose a technique to find the lowest core speed to schedule individual tasks. The proposed technique is experimentally evaluated and the results show the supremacy of our test over the existing counterparts. Following that, the lightest task shifting policy is adapted for balancing core utilization, which is utilized to determine the uniform system speed for a given task set. The aforementioned guarantees that: (i) all the tasks fulfill their deadlines and (ii) the overall system energy consumption is reduced.

Ada for parallel, embedded, and real-time applications

The arrival and popularity of multi-core processors has sparked a renewed interest in the development of parallel programs. Similarly, the availability of low cost microprocessors and sensors has generated a great interest in embedded real-time programs. Ada is arguably the most appropriate language for development of parallel and real-time applications. This tutorial provides an introduction to the features of Ada that make it appropriate in these domains including. High level support for low level programming. The task. Communication and synchronization based on shared objects. Communication and synchronization based on direct interaction. Support for compliance with real-time scheduling theory.