An Analysis of Lazy and Eager Limited Preemption Approaches under DAG-Based Global Fixed Priority Scheduling

DAG-based scheduling models have been shown to effectively express the parallel execution of current many-core heterogeneous architectures. However, their applicability to real-time settings is limited by the difficulties to find tight estimations of the worst-case timing parameters of tasks that may arbitrarily be preempted/migrated at any instruction. An efficient approach to increase the system predictability is to limit task preemptions to a set of pre-defined points. This limited preemption model supports two different preemption approaches, eager and lazy, which have been analyzed only for sequential task-sets. This paper proposes a new response time analysis that computes an upper bound on the lower priority blocking that each task may incur with eager and lazy preemptions. We evaluate our analysis with both, synthetic DAG-based task-sets and a real case-study from the automotive domain. Results from the analysis demonstrate that, despite the eager approach generates a higher number of priority inversions, the blocking impact is generally smaller than in the lazy approach, leading to a better schedulability performance.This work was funded by the EU projects P-SOCRATES (FP7-ICT-2013-10) and HERCULES (H2020/ICT/2015/688860), and the Spanish Ministry of Science and Innovation under contract TIN2015-65316-P.Peer ReviewedPostprint (author's final draft

Combining Time-Triggered Plans with Priority Scheduled Task Sets

The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-319-39083-3_13Time-triggered and concurrent priority-based scheduling are the two major approaches in use for real-time and embedded systems. Both approaches have their own advantages and drawbacks. On the one hand, priority-based systems facilitate separation of concerns between functional and timing requirements by relying on an underlying real- time operating system that takes all scheduling decisions at run time. But this is at the cost of indeterminism in the exact timing pattern of execution of activities, namely variable release jitter. On the other hand, time-triggered schedules are more intricate to design since all schedul- ing decisions must be taken beforehand in the design phase, but their advantage is determinism and more chances for minimisation of release jitter. In this paper we propose a software architecture that enables the combined and controlled execution of time-triggered plans and priority- scheduled tasks. We also describe the implementation of an Ada library supporting it. Our aim is to take advantage of the best of both ap- proaches by providing jitter-controlled execution of time-triggered tasks (e.g., control tasks), coexisting with a set of priority-scheduled tasks, with less demanding jitter requirements.This work has been partly supported by the Spanish Government’s project M2C2 (TIN2014-56158-C4-1-P-AR) and the European Commission’s project EMC2 (ARTEMIS-JU Call 2013 AIPP-5, Contract 621429).Real Sáez, JV.; Sáez Barona, S.; Crespo, A. (2016). Combining Time-Triggered Plans with Priority Scheduled Task Sets. En Reliable Software Technologies – Ada-Europe 2016. Springer. 195-212. https://doi.org/10.1007/978-3-319-39083-3_13S195212Liu, C., Layland, J.: Scheduling algorithms for multiprogramming in a hard real-time environment. J. ACM 20(1), 46–61 (1973)Martí, P., Fuertes, J., Fohler, G.: Jitter compensation for real-time control systems. In: Real-Time Systems Symposium (2001)Dobrin, R.: Combining off-line schedule construction and fixed priority scheduling in real-time computer systems. Ph.D. thesis. Mälardalen University (2005)Cervin, A.: Integrated control and real-time scheduling. Ph.D. thesis. Lund Institute of Technology, April 2003Balbastre, P., Ripoll, I., Vidal, J., Crespo, A.: A task model to reduce control delays. Real-Time Syst. 27(3), 215–236 (2004)Hong, S., Hu, X., Lemmon, M.: Reducing delay jitter of real-time control tasks through adaptive deadline adjustments. In: 22nd Euromicro Conference on Real-Time Systems - ECRTS, pp. 229–238. IEEE Computer Society (2010)ISO/IEC-JTC1-SC22-WG9: Ada Reference Manual ISO/IEC 8652:2012(E) (2012). http://www.ada-europe.org/manuals/LRM-2012.pdfBaker, T.P., Shaw, A.: The cyclic executive model and Ada. In: Proceedings IEEE Real Time Systems Symposium 1988, Huntsville, Alabama, pp. 120–129 (1988)Liu, J.W.S.: Real-Time Systems. Prentice-Hall Inc., Upper Saddle River (2000)Pont, M.J.: The Engineering of Reliable Embedded Systems: LPC1769. SafeTTy Systems Limited, Skelmersdale (2014). ISBN: 978-0-9930355-0-0Aldea Rivas, M., González Harbour, M.: MaRTE OS: an Ada kernel for real-time embedded applications. In: Strohmeier, A., Craeynest, D. (eds.) Ada-Europe 2001. LNCS, vol. 2043, pp. 305–316. Springer, Heidelberg (2001)Palencia, J., González-Harbour, M.: Schedulability analysis for tasks with static and dynamic offsets. In: 9th IEEE Real-Time Systems Symposium (1998)Wellings, A.J., Burns, A.: A framework for real-time utilities for Ada 2005. Ada Lett. XXVI XXVII(2), 41–47 (2007)Real, J., Crespo, A.: Incorporating operating modes to an Ada real-time framework. Ada Lett. 30(1), 73–85 (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

Combined Scheduling of Time-Triggered Plans and Priority Scheduled Task Sets

© Owner/Author (2016). This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in ACM SIGAda Ada Letters, 36(1), 68-76, http://dx.doi.org/10.1145/10.1145/2971571.2971580.[EN] Preemptive, priority-based scheduling on the one hand, and time-triggered scheduling on the other, are the two major techniques in use for development of real-time and embedded software. Both have their advantages and drawbacks with respect to the other, and are commonly adopted in mutual exclusion. In a previous paper, we proposed a software architecture that enables the combined and controlled execution of time-triggered plans and priority-scheduled tasks. The goal was to take advantage of the best of both approaches by providing deterministic, jitter-controlled execution of time-triggered tasks (e.g., control tasks), coexisting with a set of priority-scheduled tasks, with less demanding jitter requirements. In this paper, we briefly describe the approach, in which the time-triggered plan is executed at the highest priority level, controlled by scheduling decisions taken only at particular points in time, signalled by recurrent timing events. The rest of priority levels are used by a set of concurrent tasks scheduled by static or dynamic priorities. We also discuss several open issues such as schedulability analysis, use of the approach in multiprocessor architectures, usability in mixed-criticality systems and needed changes to make this approach Ravenscar compliant.This work has been partly supported by the Spanish Government’s project M2C2 (TIN2014-56158-C4-1-P-AR) and the European Commission’s project EMC2 (ARTEMIS-JU Call 2013 AIPP-5, Contract 621429).Real Sáez, JV.; Sáez Barona, S.; Crespo Lorente, A. (2016). Combined Scheduling of Time-Triggered Plans and Priority Scheduled Task Sets. Ada Letters. 36(1):68-76. https://doi.org/10.1145/2971571.2971580S6876361T. P. Baker and A. Shaw. The cyclic executive model and Ada. In Proceedings IEEE Real Time Systems Symposium 1988, Huntsville, Alabama, pages 120--129, 1988.P. Balbastre, I. Ripoll, J. Vidal, and A. Crespo. A Task Model to Reduce Control Delays. Real-Time Systems, 27(3):215--236, September 2004.A. Burns and R. Davis. Mixed Criticality Systems - A Review. Technical report, Depatment of Computer Science, University of York, 2013.A. Cervin. Integrated Control and Real-Time Scheduling. PhD thesis, Lund Institute of Technology, April 2003.R. Dobrin. Combining Offline Schedule Construction and Fixed Priority Scheduling in Real-Time Computer Systems. PhD thesis, Mälardalen University, 2005.S. Hong, X. Hu, and M. Lemmon. Reducing Delay Jitter of Real-Time Control Tasks through Adaptive Deadline Adjustments. In IEEE Computer Society, editor, 22nd Euromicro Conference on Real-Time Systems -- ECRTS, pages 229--238, 2010.J. W. S. Liu. Real-Time Systems. Prentice-Hall Inc., 2000.J. Palencia and M. González-Harbour. Schedulability Analysis for Tasks with Static and Dynamic Offsets. In 9th IEEE Real-Time Systems Symposium, 1998.M. J. Pont. The Engineering of Reliable Embedded Systems: LPC1769 edition. Number ISBN: 978-0-9930355-0-0. SafeTTy Systems Limited, 2014.J. Real and A. Crespo. Incorporating Operating Modes to an Ada Real-Time Framework. Ada Letters, 30(1):73--85, April 2010.J. Real, S. Sáez, and A. Crespo. Combining time-triggered plans with priority scheduled task sets. In M. Bertogna and L. M. Pinho, editors, Reliable Software Technologies -- Ada-Europe 2016, volume 9695 of Lecture Notes in Computer Science. Springer, June 2016.S. Sáez, J. Real, and A. Crespo. An integrated framework for multiprocessor, multimoded real-time applications. In M. Brorsson and L. Pinho, editors, Reliable Software Technologies -- Ada-Europe 2012, volume 7308, pages 18--34. Springer-Verlag, June 2012.S. Sáez, J. Real, and A. Crespo. Implementation of Timing-Event Anities in Ada/Linux. Ada Letters, 35(1), April 2015.A. J. Wellings and A. Burns. A Framework for Real-Time Utilities for Ada 2005. Ada Letters, XXVII(2), August 2007

A Model-Driven Co-Design Framework for Fusing Control and Scheduling Viewpoints

Model-Driven Engineering (MDE) is widely applied in the industry to develop new software functions and integrate them into the existing run-time environment of a Cyber-Physical System (CPS). The design of a software component involves designers from various viewpoints such as control theory, software engineering, safety, etc. In practice, while a designer from one discipline focuses on the core aspects of his field (for instance, a control engineer concentrates on designing a stable controller), he neglects or considers less importantly the other engineering aspects (for instance, real-time software engineering or energy efficiency). This may cause some of the functional and non-functional requirements not to be met satisfactorily. In this work, we present a co-design framework based on timing tolerance contract to address such design gaps between control and real-time software engineering. The framework consists of three steps: controller design, verified by jitter margin analysis along with co-simulation, software design verified by a novel schedulability analysis, and the run-time verification by monitoring the execution of the models on target. This framework builds on CPAL (Cyber-Physical Action Language), an MDE design environment based on model-interpretation, which enforces a timing-realistic behavior in simulation through timing and scheduling annotations. The application of our framework is exemplified in the design of an automotive cruise control system

Production/maintenance cooperative scheduling using multi-agents and fuzzy logic

Within companies, production is directly concerned with the manufacturing schedule, but other services like sales, maintenance, purchasing or workforce management should also have an influence on this schedule. These services often have together a hierarchical relationship, i.e. the leading function (most of the time sales or production) generates constraints defining the framework within which the other functions have to satisfy their own objectives. We show how the multi-agent paradigm, often used in scheduling for its ability to distribute decision-making, can also provide a framework for making several functions cooperate in the schedule performance. Production and maintenance have been chosen as an example: having common resources (the machines), their activities are actually often conflicting. We show how to use a fuzzy logic in order to model the temporal degrees of freedom of the two functions, and show that this approach may allow one to obtain a schedule that provides a better compromise between the satisfaction of the respective objectives of the two functions

Agent-based transportation planning compared with scheduling heuristics

Here we consider the problem of dynamically assigning vehicles to transportation orders that have di¤erent time windows and should be handled in real time. We introduce a new agent-based system for the planning and scheduling of these transportation networks. Intelligent vehicle agents schedule their own routes. They interact with job agents, who strive for minimum transportation costs, using a Vickrey auction for each incoming order. We use simulation to compare the on-time delivery percentage and the vehicle utilization of an agent-based planning system to a traditional system based on OR heuristics (look-ahead rules, serial scheduling). Numerical experiments show that a properly designed multi-agent system may perform as good as or even better than traditional methods

Flexible Scheduling in Multimedia Kernels: an Overview

Current Hard Real-Time (HRT) kernels have their timely behaviour guaranteed on the cost of a rather restrictive use of the available resources. This makes current HRT scheduling techniques inadequate for use in a multimedia environment where we can make a considerable profit by a better and more flexible use of the resources. We will show that we can improve the flexibility and efficiency of multimedia kernels. Therefore we introduce Real Time Transactions (RTT) with Deadline Inheritance policies for a small class of scheduling algorithms and we will evaluate these algorithms for use in a multimedia environmen

Opportunity costs calculation in agent-based vehicle routing and scheduling

In this paper we consider a real-time, dynamic pickup and delivery problem with timewindows where orders should be assigned to one of a set of competing transportation companies. Our approach decomposes the problem into a multi-agent structure where vehicle agents are responsible for the routing and scheduling decisions and the assignment of orders to vehicles is done by using a second-price auction. Therefore the system performance will be heavily dependent on the pricing strategy of the vehicle agents. We propose a pricing strategy for vehicle agents based on dynamic programming where not only the direct cost of a job insertion is taken into account, but also its impact on future opportunities. We also propose a waiting strategy based on the same opportunity valuation. Simulation is used to evaluate the benefit of pricing opportunities compared to simple pricing strategies in different market settings. Numerical results show that the proposed approach provides high quality solutions, in terms of profits, capacity utilization and delivery reliability