An Integrated Framework for Multiprocessor, Multimoded Real-Time Applications

The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-642-30598-6_2In this paper we propose an approach for building real-time systems under a combination of requirements: specification and handling of operating modes and mode changes; implementation on top of a multiprocessor platform; integration of both aspects within a common framework; and connection with schedulability analysis procedures. The proposed approach uses finite state machines to describe operating modes and transitions, and a framework of real-time utilities that implements the required behaviour in Ada 2012. Automatic code generation plays an important role: the system is derived from the functional and timing specification, and implemented according to the abstractions provided by the framework. Response time analysis enables assessing the schedulability of the different operating modes and the transitions between modes.This work was partially supported by the Vicerrectorado de Investigación of the UPV (PAID-06-10-2397), Ministerio de Ciencia e Innovación (TIN2011-28567-C03- 03) and European Union (FP7-ICT-287702)Sáez Barona, S.; Real Sáez, JV.; Crespo, A. (2012). An Integrated Framework for Multiprocessor, Multimoded Real-Time Applications. En Reliable Software Technologies – Ada-Europe 2012. Springer. 18-34. https://doi.org/10.1007/978-3-642-30598-6_21834Wellings, A.J., Burns, A.: A Framework for Real-Time Utilities for Ada 2005. Ada Letters XXVII(2) (August 2007)Real, J., Crespo, A.: Incorporating Operating Modes to an Ada Real-Time Framework. Ada Letters 30(1) (April 2010)Sáez, S., Terrasa, S., Crespo, A.: A Real-Time Framework for Multiprocessor Platforms Using Ada 2012. In: Romanovsky, A., Vardanega, T. (eds.) Ada-Europe 2011. LNCS, vol. 6652, pp. 46–60. Springer, Heidelberg (2011)Joseph, M., Pandya, P.: Finding response times in a real-time system. British Computer Society Computer Journal 29(5), 390–395 (1986)Audsley, N., Burns, A., Richardson, M., Tindell, K., Wellings, A.J.: Applying new scheduling theory to static priority pre-emptive scheduling. Software Engineering Journal 8(5), 284–292 (1993)Real, J., Crespo, A.: Mode Change Protocols for Real-Time Systems: A Survey and a new Proposal. Real-Time Systems 26(2), 161–197 (2004)Harel, D.: Statecharts: A visual formalism for complex systems. The Science of Computer Programming 8(3), 231–274 (1987)Object Management Group: Unified Modeling Language (OMG UML) V2.4 (August 2011), http://www.omg.org/spec/UML/2.4.1Sáez, S., Terrasa, S., Lorente, V., Crespo, A.: Implementing Reactive Systems with UML State Machines and Ada 2005. In: Kordon, F., Kermarrec, Y. (eds.) Ada-Europe 2009. LNCS, vol. 5570, pp. 149–163. Springer, Heidelberg (2009)Burns, A., Wellings, A.J.: Dispatching Domains for Multiprocessor Platforms and their Representation in Ada. In: Real, J., Vardanega, T. (eds.) Ada-Europe 2010. LNCS, vol. 6106, pp. 41–53. Springer, Heidelberg (2010)Barnett, J.: State Chart XML (SCXML): State Machine Notation for Control Abstraction (May 2008), http://www.w3.org/TR/scxml

Least space-time first scheduling algorithm : scheduling complex tasks with hard deadline on parallel machines

Both time constraints and logical correctness are essential to real-time systems and failure to specify and observe a time constraint may result in disaster. Two orthogonal issues arise in the design and analysis of real-time systems: one is the specification of the system, and the semantic model describing the properties of real-time programs; the other is the scheduling and allocation of resources that may be shared by real-time program modules. The problem of scheduling tasks with precedence and timing constraints onto a set of processors in a way that minimizes maximum tardiness is here considered. A new scheduling heuristic, Least Space Time First (LSTF), is proposed for this NP-Complete problem. Basic properties of LSTF are explored; for example, it is shown that (1) LSTF dominates Earliest-Deadline-First (EDF) for scheduling a set of tasks on a single processor (i.e., if a set of tasks are schedulable under EDF, they are also schedulable under LSTF); and (2) LSTF is more effective than EDF for scheduling a set of independent simple tasks on multiple processors. Within an idealized framework, theoretical bounds on maximum tardiness for scheduling algorithms in general, and tighter bounds for LSTF in particular, are proven for worst case behavior. Furthermore, simulation benchmarks are developed, comparing the performance of LSTF with other scheduling disciplines for average case behavior. Several techniques are introduced to integrate overhead (for example, scheduler and context switch) and more realistic assumptions (such as inter-processor communication cost) in various execution models. A workload generator and symbolic simulator have been implemented for comparing the performance of LSTF (and a variant -- LSTF+) with that of several standard scheduling algorithms. LSTF\u27s execution model, basic theories, and overhead considerations have been defined and developed. Based upon the evidence, it is proposed that LSTF is a good and practical scheduling algorithm for building predictable, analyzable, and reliable complex real-time systems. There remain some open issues to be explored, such as relaxing some current restrictions, discovering more properties and theorems of LSTF under different models, etc. We strongly believe that LSTF can be a practical scheduling algorithm in the near future

Going Beyond Deadline-Driven Low-level Scheduling in Distributed Real-Time Computing Systems

Abstract: In real-time computing systems, timing-requirement specifications coming from the application designer are the obvious primary driver for resource allocation. Deadline-driven scheduling of computation-segments has been studied as an advanced mode of scheduling devised to meet the timing requirement specifications. However, it does not reflect additional concerns of the application designer, the damaging impacts of various timing violations on the application. The notion of risk-incursion function (RIF) as a framework for specification of such damaging impacts has been established by the first co-author. In this paper, a concrete implementation approach of the RIFdriven resource allocation scheme is discussed first. Then two RIF-based scheduling algorithms are discussed. The results of the experiment conducted to compare the performance of RIF-based scheduling algorithms against that of deadline-driven scheduling algorithms are also provided

Real-Time Model Checking Support for AADL

We describe a model-checking toolchain for the behavioral verification of AADL models that takes into account the realtime semantics of the language and that is compatible with the AADL Behavioral Annex. We give a high-level view of the tools and transformations involved in the verification process and focus on the support offered by our framework for checking user-defined properties. We also describe the experimental results obtained on a significant avionic demonstrator, that models a network protocol in charge of data communications between an airplane and ground stations

MorphoSys: efficient colocation of QoS-constrained workloads in the cloud

In hosting environments such as IaaS clouds, desirable application performance is usually guaranteed through the use of Service Level Agreements (SLAs), which specify minimal fractions of resource capacities that must be allocated for unencumbered use for proper operation. Arbitrary colocation of applications with different SLAs on a single host may result in inefficient utilization of the host’s resources. In this paper, we propose that periodic resource allocation and consumption models -- often used to characterize real-time workloads -- be used for a more granular expression of SLAs. Our proposed SLA model has the salient feature that it exposes flexibilities that enable the infrastructure provider to safely transform SLAs from one form to another for the purpose of achieving more efficient colocation. Towards that goal, we present MORPHOSYS: a framework for a service that allows the manipulation of SLAs to enable efficient colocation of arbitrary workloads in a dynamic setting. We present results from extensive trace-driven simulations of colocated Video-on-Demand servers in a cloud setting. These results show that potentially-significant reduction in wasted resources (by as much as 60%) are possible using MORPHOSYS.National Science Foundation (0720604, 0735974, 0820138, 0952145, 1012798

A survey on formal specification and verification of separation kernels

Separation kernels are fundamental software of safety and security-critical systems, which provide to their hosted applications spatial and temporal separation as well as controlled information flows among partitions. The application of separation kernels in critical domain demands the correctness of the kernel by formal verification. To the best of our knowledge, there is no survey paper on this topic. This paper presents an overview of formal specification and verification of separation kernels. We first present the background including the concept of separation kernel and the comparisons among different kernels. Then, we survey the state of the art on this topic since 2000. Finally, we summarize research work by detailed comparison and discussion

The Epistemology of scheduling problems

Scheduling is a knowledge-intensive task spanning over many activities in day-to-day life. It deals with the temporally-bound assignment of jobs to resources. Although scheduling has been extensively researched in the AI community for the past 30 years, efforts have primarily focused on specific applications, algorithms, or 'scheduling shells' and no comprehensive analysis exists on the nature of scheduling problems, which provides a formal account of what scheduling is, independently of the way scheduling problems can be approached. Research on KBS development by reuse makes use of ontologies, to provide knowledge-level specifications of reusable KBS components. In this paper we describe a task ontology, which formally characterises the nature of scheduling problems, independently of particular application domains and in-dependently of how the problems can be solved. Our results provide a comprehensive, domain-independent and formally specified refer-ence model for scheduling applications. This can be used as the ba-sis for further analyses of the class of scheduling problems and also as a concrete reusable resource to support knowledge acquisition and system development in scheduling applications

An ERP Implementation Method : Studying a Pharmaceutical Company

Analysing the development process for an ERP solution, in our case SAP, is one of the most critical processes in implementing standard software packages. Modelling of the proposed system can facilitate the development of enterprise systems not from scratch but through use of predefined parts who represents the best knowledge captured from numerous case studies. This aim at abstracting the specification of the required information system as well as modelling the process towards this goal. Modelling plays a central role in the organisation of the information systems development process and the information systems community has developed a large number of conceptual models, systems of concepts, for representing conceptual schemata. In the area of ERP systems, because of the characteristics that distinguishes them, conceptual modelling can help in all aspects of the development process, from goal elicitation to reuse of the captured knowledge, through the use of the appropriate modelling schemata. SAP offers a standardised software solution, thus making easier the alignment of SAP requirements to enterprise requirements in a goal form, and the correspondent business processes

On the free, safe, and timely execution of component-based systems

Traditional real-time systems are reluctant to integrate dynamic behavior since it challenges predictability and timeliness. Current efforts are starting to address the inclusion of a controllable level of dynamicity in real-time systems to increase the degree of freedom or flexibility in the execution of real-time systems. This is mainly achieved by imposing a set of bounds and limitations to the allowed system structure and operations during a transition. The ultimate goal is to time-bound the duration and result of the system state transitions. One of the main obstacles for run-time transitions is the difficulty in characterizing the different operations and phases of a run-time system transition to guarantee a time bound for each phase. In this paper, an infrastructure is described to ensure the timely execution of state transitions that can be safely incorporated and performed at run-time in a component-based real-time system, preserving its temporal properties. The infrastructure allows to perform different management operations to modify components at run-time ensuring the overall schedulability of the system. The infrastructure is validated by its implementation in a specific component-based framework