2014 IEEE Real-Time Systems Symposium最新文献

{"title":"Linux's Processor Affinity API, Refined: Shifting Real-Time Tasks Towards Higher Schedulability","authors":"Felipe Cerqueira, A. Gujarati, Björn B. Brandenburg","doi":"10.1109/RTSS.2014.29","DOIUrl":"https://doi.org/10.1109/RTSS.2014.29","url":null,"abstract":"Virtually all major real-time operating systems such as QNX, VxWorks, LynxOS, and most real-time variants of Linux expose processor affinity APIs to restrict task migrations. Initially motivated by throughput and isolation reasons, the ability to flexibly control migrations on a per-task basis has also proved to be useful from a schedulability perspective. However, as the motivation to use processor affinities is highly application-specific, the two interests can conflict, i.e., The fixed, user-specified processor affinities chosen for non-schedulability reasons can actually limit any possible gains in schedulability. This paper specifically addresses the scenario where processor affinities are given as input, and investigates the following question: while maintaining API compatibility (i.e., Without changing the interface exposed to the programmer), is it possible to improve schedulability beyond what Linux and Linux-like systems currently offer, without violating the original affinity restrictions? To answer this question, we explore the similarities between priority-based scheduling with processor affinities and the assignment problem with seniority and job priority constraints, studied previously by Caron et al. In an operations-research context, to derive a more generic model of migrations. Based on vertex-weighted bipartite matchings, the proposed model exploits the idea of shifting high-priority tasks among processors in their affinity set, in order to accommodate lower-priority tasks that have more constrained processor affinities. The proposed approach is analyzed with a novel shifting-aware schedulability analysis based on linear programming. An empirical evaluation in terms of schedulability shows shifting to be effective, although performance naturally degrades if migration overheads are high.","PeriodicalId":353167,"journal":{"name":"2014 IEEE Real-Time Systems Symposium","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125864552","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}

{"title":"MC-Fluid: Fluid Model-Based Mixed-Criticality Scheduling on Multiprocessors","authors":"Jaewoo Lee, Kieu-My Phan, Xiaozhe Gu, Jiyeon Lee, A. Easwaran, I. Shin, Insup Lee","doi":"10.1109/RTSS.2014.32","DOIUrl":"https://doi.org/10.1109/RTSS.2014.32","url":null,"abstract":"A mixed-criticality system consists of multiple components with different criticalities. While mixed-criticality scheduling has been extensively studied for the uniprocessor case, the problem of efficient scheduling for the multiprocessor case has largely remained open. We design a fluid model-based multiprocessor mixed-criticality scheduling algorithm, called MC-Fluid, in which each task is executed in proportion to its criticality-dependent rate. We propose an exact schedulability condition for MC-Fluid and an optimal assignment algorithm for criticality-dependent execution rates with polynomial complexity. Since MC-Fluid cannot construct a schedule on real hardware platforms due to the fluid assumption, we propose MC-DP-Fair algorithm, which can generate a non-fluid schedule while preserving the same schedulability properties as MC-Fluid. We show that MC-Fluid has a speedup factor of (1 + v 5)/2 ( 1.618), which is best known in multiprocessor MC scheduling, and simulation results show that MC-DP-Fair outperforms all existing algorithms.","PeriodicalId":353167,"journal":{"name":"2014 IEEE Real-Time Systems Symposium","volume":"80 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121028518","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}

{"title":"Fixed-Relative-Deadline Scheduling of Hard Real-Time Tasks with Self-Suspensions","authors":"Jian-Jia Chen, Cong Liu","doi":"10.1109/RTSS.2014.31","DOIUrl":"https://doi.org/10.1109/RTSS.2014.31","url":null,"abstract":"In many real-time systems, tasks may experience self-suspension delays when accessing external devices. The problem of scheduling such self-suspending tasks to meet hard deadlines on a uniprocessor is known to be NP-hard in the strong sense. Current solutions including the common suspension-oblivious approach of treating all suspensions as computation can be quite pessimistic. This paper shows that another category of scheduling algorithms, namely fixed-relative-deadline (FRD) scheduling, may yield better performance than classical schedulers such as EDF and RM, for real-time tasks that may experience one self-suspension during the execution of a task instance. We analyze a simple FRD algorithm, namely EDA, and derive corresponding pseudo-polynomial-time and linear-time schedulability tests. To analyze the quality of EDA and its schedulability tests, we analyze their resource augmentation factors, with respect to the speed-up factor that is needed to ensure the schedulability and feasibility of the resulting schedule. Specifically, the speed-up factor of EDA is 2 and 3, when referring to the optimal FRD scheduling and any feasible arbitrary scheduling, respectively. Moreover, the speed-up factor of the proposed linear-time schedulability test is 2.787 and 4.875, when referring to the optimal FRD scheduling and any feasible arbitrary scheduling, respectively. Furthermore, extensive experiments presented herein show that our proposed linear-time schedulability test improves upon prior approaches by a significant margin. To our best knowledge, for the scheduling of self-suspending tasks, these are the first results of any sort that indicate it might be possible to design good approximation algorithms.","PeriodicalId":353167,"journal":{"name":"2014 IEEE Real-Time Systems Symposium","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128110194","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}

{"title":"Generalized Decision Aggregation in Distributed Sensing Systems","authors":"Lu Su, Qi Li, Shaohan Hu, Shiguang Wang, Jing Gao, Hengchang Liu, T. Abdelzaher, Jiawei Han, Xue Liu, Yan Gao, Lance M. Kaplan","doi":"10.1109/RTSS.2014.40","DOIUrl":"https://doi.org/10.1109/RTSS.2014.40","url":null,"abstract":"In this paper, we present GDA, a generalized decision aggregation framework that integrates information from distributed sensor nodes for decision making in a resource efficient manner. Traditional approaches that target similar problems only take as input the discrete label information from individual sensors that observe the same events. Different from them, our proposed GDA framework is able to take advantage of the confidence information of each sensor about its decision, and thus achieves higher decision accuracy. Targeting generalized problem domains, our framework can naturally handle the scenarios where different sensor nodes observe different sets of events whose numbers of possible classes may also be different. GDA also makes no assumption about the availability level of ground truth label information, while being able to take advantage of any if present. For these reasons, our approach can be applied to a much broader spectrum of sensing scenarios. The advantages of our proposed framework are demonstrated through both theoretic analysis and extensive experiments.","PeriodicalId":353167,"journal":{"name":"2014 IEEE Real-Time Systems Symposium","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116968023","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}

{"title":"Fast on Average, Predictable in the Worst Case: Exploring Real-Time Futexes in LITMUSRT","authors":"R. Spliet, M. Vanga, Björn B. Brandenburg, S. Dziadek","doi":"10.1109/RTSS.2014.33","DOIUrl":"https://doi.org/10.1109/RTSS.2014.33","url":null,"abstract":"This paper explores the problem of how to improve the average-case performance of real-time locking protocols, preferably without significantly deteriorating worst-case performance. Motivated by the futex implementation in Linux, where uncontended lock operations under the Priority Inheritance Protocol (PIP) do not incur mode-switching overheads, we extend this concept to more sophisticated protocols, namely the PCP, the MPCP and the FMLP+. We identify the challenges involved in implementing futexes for these protocols and present the design and evaluation of their implementations in LITMUSRT, a real-time extension of the Linux kernel. Our evaluation shows substantial improvements in the uncontended case (e.g., A futex implementation of the PCP lowers lock acquisition and release overheads by up to 75% and 92%, respectively), at the expense of some increases in worst-case overhead on par with Linux's existing futex implementation.","PeriodicalId":353167,"journal":{"name":"2014 IEEE Real-Time Systems Symposium","volume":"2015 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127790367","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}

{"title":"Approximate Response Time Analysis of Real-Time Task Graphs","authors":"Nan Guan, Chuancai Gu, Martin Stigge, Qingxu Deng, W. Yi","doi":"10.1109/RTSS.2014.20","DOIUrl":"https://doi.org/10.1109/RTSS.2014.20","url":null,"abstract":"The response time analysis problem is intractable for most existing real-time task models, except the simplest ones. Exact solutions for this problem in general have exponential complexity, and may run into scalability problems for large-scale task systems. In this paper, we study approximate analysis for static-priority scheduling of the Digraph Real-Time task model, which is a generalization of most existing graph-based real-time task models. We present two approximate analysis methods RBF and IBF, both of which have pseudo-polynomial complexity. We quantitatively evaluate their analysis precision using the metric speedup factor. We prove that RBF has a speedup factor of 2, and this is tight even for dual-task systems. The speedup factor of IBF is an increasing function with respect to k, the number of interfering tasks. This function converges to 2 as k approaches infinity and equals 1 when k = 1, implying that the IBF analysis is exact for dual-task systems. We also conduct simulation experiments to evaluate the precision and efficiency of RBF and IBF with randomly generated task sets. Results show that the proposed approximate analysis methods have very high efficiency with low precision loss.","PeriodicalId":353167,"journal":{"name":"2014 IEEE Real-Time Systems Symposium","volume":"68 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121796582","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}

{"title":"Real-Time Discharge/Charge Rate Management for Hybrid Energy Storage in Electric Vehicles","authors":"Eugene Kim, K. Shin, Jinkyu Lee","doi":"10.1109/RTSS.2014.16","DOIUrl":"https://doi.org/10.1109/RTSS.2014.16","url":null,"abstract":"Electric vehicles (EVs) are equipped with a large number of expensive battery cells, necessitating an effective battery management system (BMS) which protects the battery cells from harsh conditions while providing the required power efficiently. The discharge/charge rate affects battery health significantly, and existing BMSes employ simple discharge/charge rate scheduling so as to prevent weak cells from excessive discharge/charge. In this paper, we design and evaluate the real-time management of battery discharge/charge rate to extend battery life for EVs based on the physical dynamics and operation history of batteries. We first explore a modern energy storage system for EVs to capture physical dynamics and their impact on the battery discharge/charge rate, for example, a regenerative braking system for reusing the dissipated energy leads to current surges into the batteries, which shortens battery life. Based on understanding of the effects of discharge/charge rate in an energy storage system, we devise control knobs for manipulating the rate. Then, we design an adaptive discharge/charge rate management algorithm that determines the control knobs with a reconfigurable energy storage architecture. Our in-depth evaluation results demonstrate that the proposed discharge/charge rate management improves battery life up to 37.7% at little additional cost over the existing energy storage systems.","PeriodicalId":353167,"journal":{"name":"2014 IEEE Real-Time Systems Symposium","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125869187","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}

{"title":"Time-Reversibility of Schedulability Tests","authors":"Jinkyu Lee","doi":"10.1109/RTSS.2014.18","DOIUrl":"https://doi.org/10.1109/RTSS.2014.18","url":null,"abstract":"For timing guarantees of a set of real-time tasks under a target scheduling algorithm, a number of schedulability tests have been studied. However, there still exist many task sets that are potentially schedulable by a target scheduling algorithm, but proven schedulable by none of existing schedulability tests, especially on a multiprocessor platform. In this paper, we propose a new notion of time-reversibility of schedulability tests, which yields tighter schedulability guarantees by viewing real-time scheduling under a change in the sign of time. To this end, we first define the notion of a time-reversed scheduling algorithm against a target scheduling algorithm, for example, the time-reversed scheduling algorithm against EDF (Earliest Deadline First) is LCFS (Last-Come, First-Served), and the converse also holds. Then, a schedulability test for a scheduling algorithm is said to be time-reversible with respect to schedulability, if all task sets deemed schedulable by the test are also schedulable by its time-reversed scheduling algorithm. To exploit the notion of time-reversibility for tighter schedulability guarantees, we not only prove time-reversibility of an existing schedulability test, but also develop a new time-reversible schedulability test, both of which cover additional schedulable task sets. Next, we generalize the time-reversibility theory towards partial execution. Utilizing the notion, we can assure the schedulability of a task under a target scheduling algorithm in a divide-and-conquer manner: (i) the first some units of execution guaranteed by a schedulability test for the scheduling algorithm, and (ii) the remaining execution guaranteed by a time-reversible (with respect to partial execution) schedulability test for its time-reversed scheduling algorithm. Such a divide-and-conquer approach has not been directly applied to existing schedulability tests in that they cannot address (ii) effectively. As a case study, this paper develops RTA (Response-Time Analysis) for LCFS, proves its time-reversibility, and applies the divide-and-conquer approach to the test along with an existing EDF schedulability test. Our simulation results show that the time-reversibility theory helps to find up to 13.1% additional EDF-schedulable task sets on a multiprocessor platform.","PeriodicalId":353167,"journal":{"name":"2014 IEEE Real-Time Systems Symposium","volume":"120 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124591522","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}

{"title":"Towards Cyber-Physical Systems in Social Spaces: The Data Reliability Challenge","authors":"Shiguang Wang, Dong Wang, Lu Su, Lance M. Kaplan, T. Abdelzaher","doi":"10.1109/RTSS.2014.19","DOIUrl":"https://doi.org/10.1109/RTSS.2014.19","url":null,"abstract":"Today's cyber-physical systems (CPS) increasingly operate in social spaces. Examples include transportation systems, disaster response systems, and the smart grid, where humans are the drivers, survivors, or users. Much information about the evolving system can be collected from humans in the loop, a practice that is often called crowd-sensing. Crowd-sensing has not traditionally been considered a CPS topic, largely due to the difficulty in rigorously assessing its reliability. This paper aims to change that status quo by developing a mathematical approach for quantitatively assessing the probability of correctness of collected observations (about an evolving physical system), when the observations are reported by sources whose reliability is unknown. The paper extends prior literature on state estimation from noisy inputs, that often assumed unreliable sources that fall into one or a small number of categories, each with the same (possibly unknown) background noise distribution. In contrast, in the case of crowd-sensing, not only do we assume that the error distribution is unknown but also that each (human) sensor has its own possibly different error distribution. Given the above assumptions, we rigorously estimate data reliability in crowd-sensing systems, hence enabling their exploitation as state estimators in CPS feedback loops. We first consider applications where state is described by a number of binary variables, then extend the approach trivially to multivalued variables. The approach also extends prior work that addressed the problem in the special case of systems whose state does not change over time. Evaluation results, using both simulation and a real-life case-study, demonstrate the accuracy of the approach.","PeriodicalId":353167,"journal":{"name":"2014 IEEE Real-Time Systems Symposium","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130782098","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}

{"title":"Bursty-Interference Analysis Techniques for Analyzing Complex Real-Time Task Models","authors":"Cong Liu, Jian-Jia Chen","doi":"10.1109/RTSS.2014.10","DOIUrl":"https://doi.org/10.1109/RTSS.2014.10","url":null,"abstract":"Due to the recent trend towards building complex real-time cyber-physical systems, system designers need to develop and choose expressive formal models for representing such systems, as the model should be adequately expressive such that it can accurately convey the relevant characteristics of the system being modeled. Compared to the classical sporadic task model, there exist a number of real-time task models that are more expressive. However, such models are often complex and thus are rather difficult to be analyzed efficiently. Due to this reason, prior analysis methods for dealing with such complex task models are pessimistic. In this paper, a novel analysis technique, namely the bur sty-interference analysis, is presented for analyzing two common expressive real-time task models, the general self-suspending task model and the deferrable server task model. This technique is used to derive new uniprocessor utilization-based schedulability tests and rate-monotonic utilization bounds for the two considered task models scheduled under rate-monotonic scheduling. Extensive experiments presented herein show that our proposed tests improve upon prior tests in all scenarios, in many cases by a wide margin. To the best of our knowledge, these are the first techniques that can efficiently analyze the general self-suspending and deferrable server task models on uniprocessors.","PeriodicalId":353167,"journal":{"name":"2014 IEEE Real-Time Systems Symposium","volume":"138 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115083584","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}