Although many cyber-physical systems are both mixed-criticality system and compositional system, there are little work on intersection of mixed-criticality system and compositional system. We propose novel concepts for task-level criticality mode and reconsider temporal isolation in terms of compositional mixed-criticality scheduling

Chwa, Hoon Sung

Easwaran, Arvind

Lee, Insup

Lee, Jaewoo

Shin, Insik

English

ScholarlyCommons@Penn

University of PennsylvaniaScholarlyCommonsDepartmental Papers (CIS) Department of Computer & Information Science12-2015Towards Compositional Mixed-Criticality Real-Time Scheduling in Open SystemsJaewoo LeeUniversity of Pennsylvania, jaewoo@cis.upenn.eduHoon Sung ChwaArvind EaswaranInsik ShinInsup LeeUniversity of Pennsylvania, lee@cis.upenn.eduFollow this and additional works at: http://repository.upenn.edu/cis_papersPart of the Computer Engineering Commons, and the Computer Sciences Commons8th International Workshop on Compositional Theory and Technology for Real-Time Embedded Systems (CRTS 2015) held in conjunction with 36thIEEE Real-Time Systems Symposium (RTSS 2015), San Antonio, Texas, December 1-4, 2015This paper is posted at ScholarlyCommons. http://repository.upenn.edu/cis_papers/819For more information, please contact repository@pobox.upenn.edu.Recommended CitationJaewoo Lee, Hoon Sung Chwa, Arvind Easwaran, Insik Shin, and Insup Lee, "Towards Compositional Mixed-Criticality Real-TimeScheduling in Open Systems", 8th International Workshop on Compositional Theory and Technology for Real-Time Embedded Systems(CRTS 2015) . December 2015.Towards Compositional Mixed-Criticality Real-Time Scheduling in OpenSystemsAbstractAlthough many cyber-physical systems are both mixed-criticality system and compositional system, there arelittle work on intersection of mixed-criticality system and compositional system. We propose novel conceptsfor task-level criticality mode and reconsider temporal isolation in terms of compositional mixed-criticalityscheduling.DisciplinesComputer Engineering | Computer SciencesComments8th International Workshop on Compositional Theory and Technology for Real-Time Embedded Systems(CRTS 2015) held in conjunction with 36th IEEE Real-Time Systems Symposium (RTSS 2015), SanAntonio, Texas, December 1-4, 2015This conference paper is available at ScholarlyCommons: http://repository.upenn.edu/cis_papers/819Towards Compositional Mixed-Criticality Real-TimeScheduling in Open SystemsInvited PaperJaewoo LeeUniversity of PennsylvaniaHoon Sung ChwaKAISTArvind EaswaranNanyang TechnologicalUniversityInsik ShinKAISTinsik.shin@cs.kaist.ac.krInsup LeeUniversity of PennsylvaniaABSTRACTAlthough many cyber-physical systems are both mixed-criticalitysystem and compositional system, there are little work onintersection of mixed-criticality system and compositionalsystem. We propose novel concepts for task-level criticality-mode and reconsider temporal isolation in terms of compo-sitional mixed-criticality scheduling.1. INTRODUCTIONAs computer technology advances, traditional real-timesystems evolve into cyber-physical systems (CPS), whichare intelligent systems sensing and actuating physical en-vironment. There are two increasing trends in CPS. Onetrend is resource sharing under a shared platform for effi-cient resource usage. Resource efficiency is important be-cause modern CPS have a large number of functions underSize, Weight, and Power (SWaP) constraint. Another trend ispartitioning for safety assurance. To minimize interferencefrom other parts of the system, we need to partition functionsof CPS.One may achieve partitioning/isolation through worst-caseresource reservation while highly reliable (and potentiallypessimistic) Worst-Case Execution Time (WCET) estimatesare used for reservation. This is ideal for achieving isolation,but not very efficient in resource utilization.The concept of mixed-criticality has been introduced toresolve effectively those two seemingly conflicting require-ments. In 2007, a Mixed-Criticality (MC) task model basedCopyright retained by the authorson multiple execution time estimates was introduced [12]with a less reliable estimate for a common scenario and amore reliable estimate for a critical scenario. Several studieshave used (and extended) the above model to develop mixed-criticality scheduling theory [3, 4, 6, 8, 12], showing that it ispossible to achieve partitioning for higher-criticality taskseven in critical scenarios, while improving resource utiliza-tion in common scenarios.Yet, there are many issues to explore to improve resourceutilization. For example, many previous studies share theassumption that all high-criticality tasks will simultaneouslyexhibit critical scenarios, and consequently suspend all low-criticality tasks. However, such an assumption is very un-likely to happen in practice. Recently, a few studies consid-ered this issue [5, 7, 9, 11] and proposed approaches to im-prove resource utilization for low-criticality tasks. We planto consider this issue for compositional mixed-criticalityscheduling in open systems.In practice, many large-scale complex CPS are constructedunder open system design, where individual components areconstructed independently from different vendors and inte-grated into the systems (e.g., ARINC [1] and AUTOSAR [2]standards). Little attention has made to efficiently schedul-ing mixed-criticality components in a compositional man-ner in open systems, except recent studies [7, 9]. Althoughtraditional temporal isolation only consider strict isolationbetween components, we plan to consider a diverse levels(degrees) of temporal isolation in consideration of mixed-criticality.2. SYSTEM MODELWe consider dual criticality: high (HI) and low (LO). Weconsider a MC task set consisting of n MC tasks. Each MCtask τi is characterized by (Ti, CLi , CHi , χi), where Ti is taskperiod, CLi is LO-criticality WCET (LO-WCET), CHi is HI-criticality WCET (HI-WCET), and χi ∈ {HI,LO} is taskcriticality level. Depending on χi, a task is either a LO-criticality task (LO-task) or a HI-criticality task (HI-task).A component consists of a set of component or a set oftasks. The system has a special component which representsworkload of the system.3. MC SCHEDULING ON INDUSTRIALPLATFORMSA demand of industry is to optimize the real-time perfor-mance of both HI- and LO-tasks in MC systems. For anexample of the automotive system with high-critical enginefunction and lower-critical communication function, the sys-tem designer wants to execute communication function asmuch as possible except emergency situation on the engine.However, existing MC schemes show low performance ofLO-tasks in terms of the ratio of meeting deadline (RMD)1.It is because existing MC schemes rely on extremely pes-simistic assumption of system-mode, which represents run-time system-level criticality-mode2. In practice, it is a rarecase that all HI-tasks execute for their HI-WCETs simulta-neously3.If we can capture a fine-grained runtime status of the sys-tem, we can reduce the pessimism of system-mode. Forthis purpose, we propose a task-level criticality-mode (calledTask-mode), which represents runtime criticality status ofevery task.Definition 1 (Task-mode). For each task, task-mode repre-sents its runtime criticality mode as follows:• When the task-mode of the task is HI, current job of thetask executes up to HI-WCET.• When the task-mode of the task is LO, current job ofthe task executes up to LO-WCET.Some initial works [5, 11] improved RMD of LO-tasksunder pessimistic system mode assumption. Overcoming thelimitation of system mode, compositional MC approaches [7,9] introduced a concept of component-mode, which repre-sents runtime criticality mode for a component. Usingcomponent-mode, they identify fine-grained execution be-haviors of jobs in a component. However, they still have pes-simism that all components request up to their HI-criticalitybudgets when a single component requests its HI-criticalitybudget [7] or all LO-tasks in a component are dropped atcomponent mode-switch [9]. Our task-mode identifies morefine-grained execution behaviors in the system. In task-modeapproach, each task has independent criticality mode and thesystem drop only minimal LO-tasks at task-mode switch.To develop a new MC scheduling algorithm with task-mode, we utilize an existing MC scheduling algorithm. EDF-VD [3] in unicore MC has a simple algorithm with the con-cept of virtual deadlines and has the speedup factor of 4/3,which is optimal. We propose EDF-VD-TM scheduling al-gorithm extending EDF-VD with task-mode. We schedule1RMD is the reverse of deadline miss ratio (DMR):RMD = 1−DMR2If the system mode is HI (LO), current jobs of all tasks mayexecute up to their HI-WCETs (LO-WCETs).3Its example can be found in Gu et al. [7].a LO-task with its real deadline. We schedule a HI-task asfollows:• If task-mode of the task is LO, the task is scheduledwith its virtual deadline.• If the task execute more than its LO-WCET, the systemswitches task-mode of the task to HI and drops LO-tasks that are necessary to schedule all HI-tasks.• If task-mode of the task is HI , the task is scheduledwith its real deadline.Difference between EDF-VD and EDF-VD-TM is handlingthe situation when a task executes more than its LO-WCET.Although EDF-VD switches system-mode to HI and dropsall LO-tasks, EDF-VD-TM switches only task-mode of thetask and drops only minimal LO-tasks for schedulability ofHI-tasks.We plan to derive schedulability analysis for EDF-VD-TM. We also plan to evaluate EDF-VD-TM in terms of RMDof LO-tasks in comparison with existing algorithms.4. MC SCHEDULING ON OPEN INDUS-TRIAL PLATFORMSMany CPS applications have characteristics of both MCsystems and compositional systems. For example, avionicsystem development is subject to ARINC standard [1] (com-posability) and DO-178B standard (MC characteristic). Re-cent MC schemes support open system design [7, 9]. In thissection, we will extend EDF-VD-TM considering open sys-tem.To extend MC scheduling into open systems, we needto revisit temporal isolation between components4. In tra-ditional compositional scheduling [10], compositional real-time guarantee is built on temporal isolation and computa-tion of component interface. In MC systems, however, tra-ditional isolation is inefficient and overly-pessimistic [7]. Ifa HI-task in a component executes more than its LO-WCET,it is allowed to drop LO-tasks inside the component (nat-urally) or even LO-tasks in other components (by mixed-criticality principle). Then, what is proper concept of isola-tion for MC components? We propose the definition of MCisolation (Def. 2).Definition 2 (MC isolation). Consider any two components:• Components are weakly isolated if HI-tasks in onecomponent may affect the correctness of LO-tasks inthe other component.• Components are strongly isolated if no tasks in onecomponent may affect the correctness of tasks in theother component (the same as traditional isolation).Recent compositional MC works also considered their iso-lation concepts [7, 9]. Ren and Phan [9] only consideredstrong isolation in their MC scheme. Gu et al. [7] intro-duced tolerance limit (TL) to determine degree of isolation4Any component cannot affect the correctness of other com-ponents.between weak isolation and strong isolation. Although Guet al. [7] consider TL as a given parameter for a component,we propose a different perspective with the concept of MCisolation.We will seek a proper MC isolation for any two compo-nents. If components are designed in the same standard (spe-cially in recognition of criticality), we can maximize RMDby using weak isolation. However, it is possible that differ-ent vendors develop different components in different stan-dard. Then, we may not allow for HI-tasks in one compo-nent to affect the correctness of LO-tasks in the other com-ponent. In this case, we can say that two components areincompatible and need to enforce strong isolation betweencomponents.To implement MC isolation, we propose a component group,which consists of compatible components. Within a com-ponent group, the system provides weak isolation betweencomponents. If two component belong to different compo-nent groups, the system provides strong isolation betweencomponents. When a new component is added, the systemseeks its compatible components. If it is not found, the sys-tem creates a new component group. As the number of com-ponent groups increases, resource efficiency of the systemdecreases while the level of safety assurance (from partition-ing) increases.We plan to extend EDF-VD-TM with the MC isolationconcept (Def. 2) and component group. We also need toderive schedulability analysis for the extended algorithm.5. REFERENCES[1] AEEC. Avionics Application Software StandardInterface: Part 1 - required services (ARINCspecification 653-2), 2006.[2] AUTOSAR. AUTomotive Open System ARchitecture.www.autosar.org.[3] S. Baruah, V. Bonifaci, G. D’Angelo, H. Li,A. Marchetti-Spaccamela, S. van der Ster, andL. Stougie. The preemptive uniprocessor schedulingof mixed-criticality implicit-deadline sporadic tasksystems. In ECRTS, 2012.[4] S. Baruah, A. Burns, and R. Davis. Response-timeanalysis for mixed criticality systems. In RTSS, 2011.[5] A. Burns and S. Baruah. Towards a more practicalmodel for mixed criticality systems. In WMC, 2013.[6] P. Ekberg and W. Yi. Bounding and shaping thedemand of mixed-criticality sporadic tasks. In ECRTS,2012.[7] X. Gu, A. Easwaran, K.-M. Phan, and I. Shin.Resource efficient isolation mechanisms inmixed-criticality scheduling. In ECRTS, 2015.[8] J. Lee, K.-M. Phan, X. Gu, J. Lee, A. Easwaran,I. Shin, and I. Lee. Mc-fluid: Fluid model-basedmixed-criticality scheduling on multiprocessors. InRTSS, 2014.[9] J. Ren and L. T. X. Phan. Mixed-criticality schedulingon multiprocessors using task grouping. In ECRTS,2015.[10] I. Shin and I. Lee. Periodic resource model forcompositional real-time guarantees. In RTSS, 2003.[11] H. Su and D. Zhu. An elastic mixed-criticality taskmodel and its scheduling algorithm. In DATE, 2013.[12] S. Vestal. Preemptive scheduling of multi-criticalitysystems with varying degrees of execution timeassurance. In RTSS, 2007.

Towards Compositional Mixed-Criticality Real-Time Scheduling in Open Systems

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Towards Compositional Mixed-Criticality Real-Time Scheduling in Open Systems

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