The problem of scheduling a set of tasks on a multiprocessor architecture is addressed. Tasks are assumed to be sporadic with arbitrary deadlines and may migrate between processors. The execution of migrating tasks is controlled by a bandwidth reservation scheme so that schedulability is guaranteed by EDF. Task migration costs are taken into consideration. Results from experiments indicate that the proposed approach performs well in terms of schedulability.
{"title":"A Bandwidth Reservation Strategy for Multiprocessor Real-Time Scheduling","authors":"Ernesto Massa, George Lima","doi":"10.1109/RTAS.2010.35","DOIUrl":"https://doi.org/10.1109/RTAS.2010.35","url":null,"abstract":"The problem of scheduling a set of tasks on a multiprocessor architecture is addressed. Tasks are assumed to be sporadic with arbitrary deadlines and may migrate between processors. The execution of migrating tasks is controlled by a bandwidth reservation scheme so that schedulability is guaranteed by EDF. Task migration costs are taken into consideration. Results from experiments indicate that the proposed approach performs well in terms of schedulability.","PeriodicalId":356388,"journal":{"name":"2010 16th IEEE Real-Time and Embedded Technology and Applications Symposium","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125332960","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Many safety-critical embedded systems are subject to certification requirements; some systems may be required to meet multiple sets of certification requirements, from different certification authorities. Certification requirements in such "mixed-criticality" systems give rise to some interesting scheduling problems, that cannot be satisfactorily addressed using techniques from conventional scheduling theory. In this paper, we propose a formal model for representing such mixed-criticality workloads. We demonstrate the intractability of determining whether a system specified in this model can be scheduled to meet all its certification requirements. For dual-criticality systems -- systems subject to two sets of certification requirements -- we quantify, via the metric of processor speedup factor, the effectiveness of 2 techniques (reservation-based scheduling and priority-based scheduling) that are widely used in scheduling such mixed-criticality systems.
{"title":"Towards the Design of Certifiable Mixed-criticality Systems","authors":"Sanjoy Baruah, Haohan Li, L. Stougie","doi":"10.1109/RTAS.2010.10","DOIUrl":"https://doi.org/10.1109/RTAS.2010.10","url":null,"abstract":"Many safety-critical embedded systems are subject to certification requirements; some systems may be required to meet multiple sets of certification requirements, from different certification authorities. Certification requirements in such \"mixed-criticality\" systems give rise to some interesting scheduling problems, that cannot be satisfactorily addressed using techniques from conventional scheduling theory. In this paper, we propose a formal model for representing such mixed-criticality workloads. We demonstrate the intractability of determining whether a system specified in this model can be scheduled to meet all its certification requirements. For dual-criticality systems -- systems subject to two sets of certification requirements -- we quantify, via the metric of processor speedup factor, the effectiveness of 2 techniques (reservation-based scheduling and priority-based scheduling) that are widely used in scheduling such mixed-criticality systems.","PeriodicalId":356388,"journal":{"name":"2010 16th IEEE Real-Time and Embedded Technology and Applications Symposium","volume":"45 4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129871645","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Embedded wireless networks have largely focused on open-loop sensing and monitoring. To address actuation in closed-loop wireless control systems there is a strong need to re-think the communication architectures and protocols for reliability, coordination and control. As the links, nodes and topology of wireless systems are inherently unreliable, such time-critical and safety-critical applications require programming abstractions and runtime systems where the tasks are assigned to the sensors, actuators and controllers as a single component rather than statically mapping a set of tasks to a specific physical node at design time. To this end, we introduce the Embedded Virtual Machine (EVM), a powerful and flexible programming abstraction where virtual components and their properties are maintained across node boundaries. In the context of process and discrete control, an EVM is the distributed runtime system that dynamically selects primary-backup sets of controllers to guarantee QoS given spatial and temporal constraints of the underlying wireless network. The EVM architecture defines explicit mechanisms for control, data and fault communication within the virtual component. EVM-based algorithms introduce new capabilities such as predictable outcomes and provably minimal graceful degradation during sensor/actuator failure, adaptation to mode changes and runtime optimization of resource consumption. Through case studies in process control we demonstrate the preliminary capabilities of EVM-based wireless networks.
{"title":"Embedded Virtual Machines for Robust Wireless Control and Actuation","authors":"M. Pajic, R. Mangharam","doi":"10.1109/RTAS.2010.43","DOIUrl":"https://doi.org/10.1109/RTAS.2010.43","url":null,"abstract":"Embedded wireless networks have largely focused on open-loop sensing and monitoring. To address actuation in closed-loop wireless control systems there is a strong need to re-think the communication architectures and protocols for reliability, coordination and control. As the links, nodes and topology of wireless systems are inherently unreliable, such time-critical and safety-critical applications require programming abstractions and runtime systems where the tasks are assigned to the sensors, actuators and controllers as a single component rather than statically mapping a set of tasks to a specific physical node at design time. To this end, we introduce the Embedded Virtual Machine (EVM), a powerful and flexible programming abstraction where virtual components and their properties are maintained across node boundaries. In the context of process and discrete control, an EVM is the distributed runtime system that dynamically selects primary-backup sets of controllers to guarantee QoS given spatial and temporal constraints of the underlying wireless network. The EVM architecture defines explicit mechanisms for control, data and fault communication within the virtual component. EVM-based algorithms introduce new capabilities such as predictable outcomes and provably minimal graceful degradation during sensor/actuator failure, adaptation to mode changes and runtime optimization of resource consumption. Through case studies in process control we demonstrate the preliminary capabilities of EVM-based wireless networks.","PeriodicalId":356388,"journal":{"name":"2010 16th IEEE Real-Time and Embedded Technology and Applications Symposium","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128677110","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Some real-time kernels (such as a recent real-time version of Linux) permit to execute interrupt handlers in dedicated threads, to control their interference on real-time applications. However, from the stand-point of real-time analysis, such threads are challenging and cannot be dealt with in the traditional ways. Furthermore, the application of traditional scheduling solutions (such as fixed priorities) proves ineffective in striking a good trade-off between predictability and hardware performance. This paper shows how the problem can be tackled by using the resource reservation abstraction and an appropriate model for schedulability analysis.
{"title":"Reservation-Based Interrupt Scheduling","authors":"Nicola Manica, Luca Abeni, L. Palopoli","doi":"10.1109/RTAS.2010.25","DOIUrl":"https://doi.org/10.1109/RTAS.2010.25","url":null,"abstract":"Some real-time kernels (such as a recent real-time version of Linux) permit to execute interrupt handlers in dedicated threads, to control their interference on real-time applications. However, from the stand-point of real-time analysis, such threads are challenging and cannot be dealt with in the traditional ways. Furthermore, the application of traditional scheduling solutions (such as fixed priorities) proves ineffective in striking a good trade-off between predictability and hardware performance. This paper shows how the problem can be tackled by using the resource reservation abstraction and an appropriate model for schedulability analysis.","PeriodicalId":356388,"journal":{"name":"2010 16th IEEE Real-Time and Embedded Technology and Applications Symposium","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116139428","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Recent results have shown that the feasibility problem of scheduling periodic tasks with self-suspensions is NP-hard in the strong sense. We observe that a variation of the problem statement that includes sporadic tasks instead of periodic tasks results in a simple characterization of the critical scheduling instant. This in turn leads to an exact characterization of the critical instant for self-suspending tasks with respect to the interference (preemption) from higher-priority sporadic tasks. Using this characterization, we provide pseudo-polynomial response-time tests for analyzing the schedulability of such self-suspending tasks. Self-suspending tasks can also result in more worst-case interference to lower-priority tasks than their equivalent non-suspending counterparts with zero suspension intervals. Hence, we develop a dynamic slack enforcement scheme, which guarantees that the worst-case interference caused by suspending sporadic tasks is no more than the worst-case interference arising from equivalent non-suspending sporadic tasks without suspension intervals. The worst-case response time of self-suspending sporadic tasks themselves is also shown to be unaffected by dynamic slack enforcement, thereby making it optimal. In order to reduce the runtime complexity of slack enforcement, a static slack enforcement scheme is also developed. Empirical analysis of these schemes and the previously studied period enforcement algorithm shows that static slack enforcement achieves within 3% of the breakdown utilization of dynamic slack enforcement, while period enforcement achieves within 14% of dynamic slack enforcement. System designers can take advantage of these different execution control policies depending on their taskset utilizations and implementation constraints.
{"title":"Scheduling Self-Suspending Real-Time Tasks with Rate-Monotonic Priorities","authors":"Karthik Lakshmanan, R. Rajkumar","doi":"10.1109/RTAS.2010.38","DOIUrl":"https://doi.org/10.1109/RTAS.2010.38","url":null,"abstract":"Recent results have shown that the feasibility problem of scheduling periodic tasks with self-suspensions is NP-hard in the strong sense. We observe that a variation of the problem statement that includes sporadic tasks instead of periodic tasks results in a simple characterization of the critical scheduling instant. This in turn leads to an exact characterization of the critical instant for self-suspending tasks with respect to the interference (preemption) from higher-priority sporadic tasks. Using this characterization, we provide pseudo-polynomial response-time tests for analyzing the schedulability of such self-suspending tasks. Self-suspending tasks can also result in more worst-case interference to lower-priority tasks than their equivalent non-suspending counterparts with zero suspension intervals. Hence, we develop a dynamic slack enforcement scheme, which guarantees that the worst-case interference caused by suspending sporadic tasks is no more than the worst-case interference arising from equivalent non-suspending sporadic tasks without suspension intervals. The worst-case response time of self-suspending sporadic tasks themselves is also shown to be unaffected by dynamic slack enforcement, thereby making it optimal. In order to reduce the runtime complexity of slack enforcement, a static slack enforcement scheme is also developed. Empirical analysis of these schemes and the previously studied period enforcement algorithm shows that static slack enforcement achieves within 3% of the breakdown utilization of dynamic slack enforcement, while period enforcement achieves within 14% of dynamic slack enforcement. System designers can take advantage of these different execution control policies depending on their taskset utilizations and implementation constraints.","PeriodicalId":356388,"journal":{"name":"2010 16th IEEE Real-Time and Embedded Technology and Applications Symposium","volume":"119 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116292676","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Liu and Layland discovered the famous utilization bound for fixed-priority scheduling on single processor systems in the 1970's. Since then, it has been a long standing open problem to find fixed-priority scheduling algorithms with the same bound for multiprocessor systems. In this paper, we present a partitioning-based fixed-priority multiprocessor scheduling algorithm with Liu and Layland's utilization bound.
{"title":"Fixed-Priority Multiprocessor Scheduling with Liu and Layland's Utilization Bound","authors":"Nan Guan, Martin Stigge, W. Yi, Ge Yu","doi":"10.1109/RTAS.2010.39","DOIUrl":"https://doi.org/10.1109/RTAS.2010.39","url":null,"abstract":"Liu and Layland discovered the famous utilization bound for fixed-priority scheduling on single processor systems in the 1970's. Since then, it has been a long standing open problem to find fixed-priority scheduling algorithms with the same bound for multiprocessor systems. In this paper, we present a partitioning-based fixed-priority multiprocessor scheduling algorithm with Liu and Layland's utilization bound.","PeriodicalId":356388,"journal":{"name":"2010 16th IEEE Real-Time and Embedded Technology and Applications Symposium","volume":"87 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121524141","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
While most prior work on multiprocessor real-time scheduling focuses on independent tasks, dependencies due to non-preemptive sections, suspensions, and pipeline-based precedence constraints are common in practice. In this paper, such complexities are considered in the context of the global earliest-deadline-first scheduling algorithm. It is shown that any periodic task system with such dependencies can be transformed into one with only suspensions in a way that preserves maximum per-task response times. This result enables analysis directed at systems with suspensions to be applied if non-preemptive sections and/or pipelines are present as well.
{"title":"Scheduling Suspendable, Pipelined Tasks with Non-Preemptive Sections in Soft Real-Time Multiprocessor Systems","authors":"Cong Liu, James H. Anderson","doi":"10.1109/RTAS.2010.12","DOIUrl":"https://doi.org/10.1109/RTAS.2010.12","url":null,"abstract":"While most prior work on multiprocessor real-time scheduling focuses on independent tasks, dependencies due to non-preemptive sections, suspensions, and pipeline-based precedence constraints are common in practice. In this paper, such complexities are considered in the context of the global earliest-deadline-first scheduling algorithm. It is shown that any periodic task system with such dependencies can be transformed into one with only suspensions in a way that preserves maximum per-task response times. This result enables analysis directed at systems with suspensions to be applied if non-preemptive sections and/or pipelines are present as well.","PeriodicalId":356388,"journal":{"name":"2010 16th IEEE Real-Time and Embedded Technology and Applications Symposium","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115775376","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Providing integrity, efficiency, and performance guarantees is a key challenge in the development of next-generation cyberphysical systems. Rather than mandating complete system verification, the Simplex Architecture provides robust designs by incorporating a supervisory controller that takes corrective action only when the system is in danger of violating a desired invariant property such as safety. The central issue in applying this approach is designing the switching logic for the supervisory controller such that it guarantees safety and at the same time is not overly conservative.Previous research in the area relied on finding Lyapunov functions for the underlying continuous dynamical system. In contrast, in this paper, we present an automatic method for solving this design problem through discrete abstractions of the underlying hybrid system and model checking. We present a case study where, in collaboration with John Deere, we use the developed approach to create the Simplex decision module for an off-road vehicle, which is formally verified as both correct and timely.
{"title":"Hybrid Cyberphysical System Verification with Simplex Using Discrete Abstractions","authors":"Stanley Bak, Ashley Greer, S. Mitra","doi":"10.1109/RTAS.2010.27","DOIUrl":"https://doi.org/10.1109/RTAS.2010.27","url":null,"abstract":"Providing integrity, efficiency, and performance guarantees is a key challenge in the development of next-generation cyberphysical systems. Rather than mandating complete system verification, the Simplex Architecture provides robust designs by incorporating a supervisory controller that takes corrective action only when the system is in danger of violating a desired invariant property such as safety. The central issue in applying this approach is designing the switching logic for the supervisory controller such that it guarantees safety and at the same time is not overly conservative.Previous research in the area relied on finding Lyapunov functions for the underlying continuous dynamical system. In contrast, in this paper, we present an automatic method for solving this design problem through discrete abstractions of the underlying hybrid system and model checking. We present a case study where, in collaboration with John Deere, we use the developed approach to create the Simplex decision module for an off-road vehicle, which is formally verified as both correct and timely.","PeriodicalId":356388,"journal":{"name":"2010 16th IEEE Real-Time and Embedded Technology and Applications Symposium","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131301404","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Prior work has shown that the global earliest-deadline-first (GEDF) scheduling algorithm ensures bounded deadline tardiness on multiprocessors with no utilization loss; therefore, GEDF may be a good candidate scheduling algorithm for soft real-time workloads. However, such workloads are often implemented assuming an average-case provisioning, and in prior tardiness-bound derivations for GEDF, worst-case execution costs are assumed. As worst-case costs can be orders of magnitude higher than average-case costs, using a worst-case provisioning may result in significant wasted processing capacity. In this paper, prior tardiness-bound derivations for GEDF are generalized so that execution times are probabilistic, and a bound on expected (mean) tardiness is derived. It is shown that, as long as the total expected utilization is strictly less than the number of available processors, the expected tardiness of every task is bounded under GEDF. The result also implies that any quantile of the tardiness distribution is also bounded.
{"title":"A Stochastic Framework for Multiprocessor Soft Real-Time Scheduling","authors":"A. Mills, James H. Anderson","doi":"10.1109/RTAS.2010.33","DOIUrl":"https://doi.org/10.1109/RTAS.2010.33","url":null,"abstract":"Prior work has shown that the global earliest-deadline-first (GEDF) scheduling algorithm ensures bounded deadline tardiness on multiprocessors with no utilization loss; therefore, GEDF may be a good candidate scheduling algorithm for soft real-time workloads. However, such workloads are often implemented assuming an average-case provisioning, and in prior tardiness-bound derivations for GEDF, worst-case execution costs are assumed. As worst-case costs can be orders of magnitude higher than average-case costs, using a worst-case provisioning may result in significant wasted processing capacity. In this paper, prior tardiness-bound derivations for GEDF are generalized so that execution times are probabilistic, and a bound on expected (mean) tardiness is derived. It is shown that, as long as the total expected utilization is strictly less than the number of available processors, the expected tardiness of every task is bounded under GEDF. The result also implies that any quantile of the tardiness distribution is also bounded.","PeriodicalId":356388,"journal":{"name":"2010 16th IEEE Real-Time and Embedded Technology and Applications Symposium","volume":"59 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123036934","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The specification of the sporadic server real-time scheduling policy in the IEEE POSIX standard is defective, and needs to be corrected. Via experiments using a POSIX sporadic server implementation under Linux, as well as simulations, we have shown and confirmed previously unreported defects. We propose and demonstrate a corrected sporadic server formulation that eliminates these defects without changes to the syntax of the API or any significant increase in implementation complexity.
{"title":"Defects of the POSIX Sporadic Server and How to Correct Them","authors":"M. Stanovich, T. Baker, An-I Wang, M. G. Harbour","doi":"10.1109/RTAS.2010.34","DOIUrl":"https://doi.org/10.1109/RTAS.2010.34","url":null,"abstract":"The specification of the sporadic server real-time scheduling policy in the IEEE POSIX standard is defective, and needs to be corrected. Via experiments using a POSIX sporadic server implementation under Linux, as well as simulations, we have shown and confirmed previously unreported defects. We propose and demonstrate a corrected sporadic server formulation that eliminates these defects without changes to the syntax of the API or any significant increase in implementation complexity.","PeriodicalId":356388,"journal":{"name":"2010 16th IEEE Real-Time and Embedded Technology and Applications Symposium","volume":"407 ","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133880463","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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