Issues in schedulability analysis of real-time systems

Embedded Systems, 2013

The construction of a design model is a critical phase in real-time systems (RTS) development as the choices made have a direct impact on timing aspects. In traditional model-based approaches, the design relies largely on the designer experience. Once the design model is constructed, a convenient schedulability test has to be found in order to ensure that the design allows the respect of the timing constraints. This late analysis does not guarantee the existence of a test for the given design and does not allow early detection of unfeasible designs. In order to overcome this problem, this chapter proposes the first UML/MARTE methodology for schedulability-aware real-time software design models construction.

Communications in Computer and Information Science, 2014

Parametric analysis is a powerful tool for designing modern embedded systems, because it permits to explore the space of design parameters, and to check the robustness of the system with respect to variations of some uncontrollable variable. In this paper, we address the problem of parametric schedulability analysis of distributed real-time systems scheduled by fixed priority. In particular, we propose two different approaches to parametric analysis: the first one is a novel technique based on classical schedulability analysis, whereas the second approach is based on model checking of Parametric Timed Automata (PTA). The proposed analytic method extends existing sensitivity analysis for single processors to the case of a distributed system, supporting preemptive and non-preemptive scheduling, jitters and unconstrained deadlines. Parametric Timed Automata are used to model all possible behaviours of a distributed system, and therefore it is a necessary and sufficient analysis. Both techniques have been implemented in two software tools, and they have been compared with classical holistic analysis on two meaningful test cases. The results show that the analytic method provides results similar to classical holistic analysis in a very efficient way, whereas the PTA approach is slower but covers the entire space of solutions.

2008 Euromicro Conference on Real-Time Systems, 2008

Task period adaptations are often used to alleviate temporal overload conditions in real-time systems. Existing frameworks assume that only task periods are adjustable and that task deadlines remain unchanged at all times. This paper formally introduces a more general real-time task model where task deadlines, which are less than or equal to task periods, are functions of task periods. This tight coupling between task deadlines and task periods has been discussed in a recent work in control systems and presents a novel real-time scheduling challenge. To solve the period and deadline selection problem, this article identifies a feasible period-deadline combination and proposes a heuristic, which iteratively adjusts task periods and deadlines in such a way that the task set becomes schedulable. Experimental results show that the heuristic finds a solution to the period and deadline selection problem over 73% of the time, using less than three search iterations. When it is unable to find a solution to the problem, the heuristic requires less than 0.02s to run in the worstcase (with at most 100 search iterations).

Proceedings of the 10th International Conference on Software Engineering and Applications, 2015

Transforming a software functional model that describes the underlying application to a concurrency model is considered as a critical issue in the model-based approaches for Real-Time Embedded Systems (RTES) development process. The formal methods have proven to be useful for making the development process reliable at a high abstraction level. Based on this approach, this current research proposes a generic approach to task construction that allows early detection of unfeasible design. Having a component-oriented specification as entry, the first stage of the methodology consists in the workload model specification. The workload model represents the system end-to-end computations triggered by an external stimulus and subject to hard real-time constraints. This model is then mapped into a Petri Nets formalism to perform Pinvariant method and generate all transactions in an optimized way. The refinement of the transaction set in a Schedulability Analysis Model defining an optimized threading strategy model. The latter presents the set of units of execution taken into account by the scheduler of the system and their scheduling parameters. We illustrate the advantages and effectiveness of the proposed method by constructing a concurrency model for a combined Cruise Control System and Anti-lock Braking System.

1998

We propose a unifying method for analysis of scheduling problems in real-time systems. The method is based on ACSR-VP, a real-time process algebra with value-passing capabilities. We use ACSR-VP to describe an instance of a scheduling problem as a process that has parameters of the problem as free variables. The specification is analyzed by means of a symbolic algorithm. The outcome of the analysis is a set of equations, a solution to which yields the values of the parameters that make the system schedulable. Equations are solved using integer programming or constraint logic programming. The paper presents specifications of two scheduling problems as examples.

Journal of Systems and Software, 2018

In automotive embedded real-time systems, such as the engine control unit, there are tasks that are activated whenever the crankshaft arrives at a specific angular position. As a consequence the frequency of activation changes with the crankshaft's angular speed (i.e., engine rpm). Additionally, execution times and deadlines may also depend on angular speeds and positions. This paper provides a survey on schedulability analysis techniques for tasks with this rate-dependent behaviour. It covers different task-models and analysis methods for both fixed priority and earliest deadline first scheduling. A taxonomy of the different analysis methods, classifying them according to the assumptions made and the precision of the analysis, is provided at the end of the paper.

IEEE Transactions on Software Engineering, 1994

This paper considers the problem of timing analysis for a quite general hard real-time periodic task set on a uniprocessor using fixed priority methods. Periodic tasks are decomposed into serially executed subtasks, where each subtask is characterized by an execution time, a fixed priority, and a deadline. A method for determining the schedulability of each task is presented along with its theoretical underpinnings. This method can be used to analyze the schedulability of complex task sets which involve interrupts, certain synchronization protocols, nonpreemptible sections, certain precedence constraints, and, in general, any mechanism that contributes to a complex priority structure. The method is illustrated with a realistic example.

Real-Time Systems, 2003

The usage of formal description techniques (FDTs) has arisen as a promising way of dealing with the increasing complexity of embedded real-time systems. However, FDTs do not take into account non-functional aspects, such as the time requirements, that are especially important in the context of this kind of system. In this paper, we present how to integrate real-time analysis in the context of the speci®cation and description language (SDL) FDT. In order to get this integration a real-time execution model for SDL is presented to allow us to express hard real-time constraints and solve SDL real-time anomalies as priority inversion and the access to shared resources. Based on this model, a schedulability analysis for systems specifed in SDL is proposed. Additionally, a set of SDL design techniques are proposed to redesign the system to meet the imposed deadlines in case the system does not meet them. To illustrate our proposals, an example of a computerized numerical control (CNC) machine is presented.

1998

We present an improvement of the schedulability analysis technique for distributed hard real time systems that allows us to increase the maximum schedulable resource utilization. Since the improvement affects only the analysis technique, there is no additional implementation cost for the application itself. The improvement in the analysis consists of calculating a lower bound for the best case response time of tasks and messages, in order to reduce the estimated jitter in the activation of subsequent tasks and messages. This reduction of jitter implies reduced worst case bounds for the response times, and thus allows us to increase the maximum schedulable utilization. The paper explores two different ways to calculate a lower bound on the best case execution times. The paper also shows the results of simulations that we have carried out, in which we found that we could increase the maximum schedulable limit of the different resources by approximately 5% more utilization

Proceedings 16th International Parallel and Distributed Processing Symposium, 2002

Schedulability Analysis (SA) approaches that are based on a priori information and use fixed execution times with constant workloads work well in many application domains and allow pre-deployment guarantees of real-time performance such as Rate Monotonic Analysis (RMA [2]). However, certain realtime applications must operate in highly dynamic environments, thereby precluding accurate characterization of workloads by static models. This leads to the notion that a new SA trigger for dynamic environments, in which applications experience large variations in the workload, needs to guarantee real-time performance during run-time. This paper examines the case of periodic, dynamic real-time systems, and describes an efficient SA policing technique which can trigger SA appropriately, and uses a dynamic threshold which becomes sensitive when the quality of service (QoS) of the dynamic real-time application approaches its deadline.

IEEE Transactions on Parallel and Distributed Systems, 2000

This paper addresses the schedulability problem of periodic and sporadic real-time task sets with constrained deadlines preemptively scheduled on a multiprocessor platform composed by identical processors. We assume that a global work-conserving scheduler is used and migration from one processor to another is allowed during task lifetime. First, a general method to derive schedulability conditions for multiprocessor real-time systems will be presented. The analysis will be applied to two typical scheduling algorithms: Earliest Deadline First (EDF) and Fixed Priority (FP). Then, the derived schedulability conditions will be tightened, refining the analysis with a simple and effective technique that significantly improves the percentage of accepted task sets. The effectiveness of the proposed test is shown through an extensive set of synthetic experiments. activities are in real-time scheduling theory and its application to real-time operating systems, soft real-time systems for multimedia applications and component-based real-time systems. He has been member of the program committes of many conferences in the field. He is currently Associate Editor of IEEE Transactions on Computers.

Real-Time and Embedded Technology and Applications, IEEE Symposium, 2008

Message Sequence Charts (MSCs) are widely used for describing interaction scenarios between the components of a distributed system. Consequently, worst-case response time estimation and schedulability analysis of MSC-based specifications form natural building blocks for designing distributed real-time systems. However, currently there ex- ists a large gap between the timing and quantitative per- formance analysis techniques that exist in the real-time

SICS Software-Intensive Cyber-Physical Systems, 2021

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.

Lecture Notes in Computer Science, 2006

In this paper, we address the problem of schedulability analysis of a set of real-time periodic (or sporadic) tasks on multiprocessor hardware platforms, under fixed priority global scheduling. In a multiprocessor system with M processors, a global scheduler consists of a single queue of ready tasks for all processors, and the scheduler selects the first M tasks to execute on the M processors. We allow preemption and migration of tasks between processors. This paper presents two different contributions. First, we derive a sufficient schedulability test for periodic and sporadic task system scheduled with fixed priority when priorities are assigned according to Deadline Monotonic. This test is efficient when dealing with heavy tasks (i.e. tasks with high utilization). Then, we develop an independent analysis for preperiod deadline systems. This leads to a new schedulability test with density and utilization bounds that are tighter than the existing ones.

… OF YORK DEPARTMENT OF COMPUTER SCIENCE- …, 1997

Predictability and fault tolerance are major requirements for complex real-time systems, which are either safety or mission critical. Traditionally fault tolerant techniques were employed to tackle the problem of ensuring correctness in the value domain only.