Pub Date : 1998-10-27DOI: 10.1109/RTCSA.1998.726408
Anita Mittal, G. Manimaran, C. Murthy
Many time critical applications require predictable performance and tasks in these applications have deadlines to be met. For tasks with hard deadlines, a deadline miss can be catastrophic, while for QoS degradable tasks (soft real time tasks) timely approximate results of poorer quality or occasional deadline misses are acceptable. Imprecise computation and (m,k) firm guarantee are two workload models that quantify the trade off between schedulability and result quality. We propose dynamic scheduling algorithms for integrated scheduling of real time tasks, represented by these workload models, in multiprocessor systems. The algorithms aim at improving the schedulability of tasks by exploiting the properties of these models in QoS degradation. We also show how the proposed algorithms can be adapted for integrated scheduling of multimedia streams and hard real time tasks, and demonstrate their effectiveness in quantifying QoS degradation. Through simulation, we evaluate the performance of these algorithms using the metrics-success ratio (measure of schedulability) and quality. Our simulation results show that one of the proposed algorithms, multilevel degradation algorithm, outperforms the others in terms of both the performance metrics.
{"title":"Integrated dynamic scheduling of hard and QoS degradable real-time tasks in multiprocessor systems","authors":"Anita Mittal, G. Manimaran, C. Murthy","doi":"10.1109/RTCSA.1998.726408","DOIUrl":"https://doi.org/10.1109/RTCSA.1998.726408","url":null,"abstract":"Many time critical applications require predictable performance and tasks in these applications have deadlines to be met. For tasks with hard deadlines, a deadline miss can be catastrophic, while for QoS degradable tasks (soft real time tasks) timely approximate results of poorer quality or occasional deadline misses are acceptable. Imprecise computation and (m,k) firm guarantee are two workload models that quantify the trade off between schedulability and result quality. We propose dynamic scheduling algorithms for integrated scheduling of real time tasks, represented by these workload models, in multiprocessor systems. The algorithms aim at improving the schedulability of tasks by exploiting the properties of these models in QoS degradation. We also show how the proposed algorithms can be adapted for integrated scheduling of multimedia streams and hard real time tasks, and demonstrate their effectiveness in quantifying QoS degradation. Through simulation, we evaluate the performance of these algorithms using the metrics-success ratio (measure of schedulability) and quality. Our simulation results show that one of the proposed algorithms, multilevel degradation algorithm, outperforms the others in terms of both the performance metrics.","PeriodicalId":142319,"journal":{"name":"Proceedings Fifth International Conference on Real-Time Computing Systems and Applications (Cat. No.98EX236)","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131419305","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}
Pub Date : 1998-10-27DOI: 10.1109/RTCSA.1998.726429
Lihchyun Shu
Abort-oriented protocols for hard real-time systems were proposed mainly to cope with the situation when block-at-most-once property provided by pure locking protocols such as priority ceiling protocol and stack resource protocol is incapable of scheduling a given transaction set due to excessive blocking. The underlying principle is to abort a transaction if it causes other higher-priority transactions unschedulable due to excessive blocking. By aborting the lower-priority transaction, what we gain is reduced blocking for higher-priority transactions, but what we must pay for is to re-execute the aborted lower-priority transaction. To guarantee schedulability for the whole transaction set, we must put an upper bound on the re-execution costs. In this paper, we use a tree-structured transaction framework adapted from Chakravarthy et al. (1998) and we roll back aborted transactions partially in an attempt to more accurately characterize and to reduce re-execution costs for aborted transactions.
{"title":"A characterization of re-execution costs for real-time abort-oriented protocols","authors":"Lihchyun Shu","doi":"10.1109/RTCSA.1998.726429","DOIUrl":"https://doi.org/10.1109/RTCSA.1998.726429","url":null,"abstract":"Abort-oriented protocols for hard real-time systems were proposed mainly to cope with the situation when block-at-most-once property provided by pure locking protocols such as priority ceiling protocol and stack resource protocol is incapable of scheduling a given transaction set due to excessive blocking. The underlying principle is to abort a transaction if it causes other higher-priority transactions unschedulable due to excessive blocking. By aborting the lower-priority transaction, what we gain is reduced blocking for higher-priority transactions, but what we must pay for is to re-execute the aborted lower-priority transaction. To guarantee schedulability for the whole transaction set, we must put an upper bound on the re-execution costs. In this paper, we use a tree-structured transaction framework adapted from Chakravarthy et al. (1998) and we roll back aborted transactions partially in an attempt to more accurately characterize and to reduce re-execution costs for aborted transactions.","PeriodicalId":142319,"journal":{"name":"Proceedings Fifth International Conference on Real-Time Computing Systems and Applications (Cat. No.98EX236)","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125031172","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}
Pub Date : 1998-10-27DOI: 10.1109/RTCSA.1998.726423
Sungyoung Lee, S. Oh, Chul Hee Woo
Real time multiprocessor systems frequently assume that there exists a dedicated processor for task allocation that never fails. This assumption is, however too strong in the sense that all the physical objects are subject to failure. Moreover once the dedicated processor fails, the whole multiprocessor system will fail. As a way to solve this problem, we propose a fault tolerant scheduling algorithm based on moving dual token. While the primary processor holding a primary token performs task allocation, the backup processor holding a backup token, in case the primary processor fails, does primary processor creation. Since no dedicated processor for task allocation exists in this scheme, failure of the whole multiprocessor system due to that of the dedicated processor can be avoided. In addition, the deadline friendly scheduling policy used for backup task allocation, compared to heuristic scheduling, allows easier implementation and improved scheduling predictability. Simulation results show that the proposed dual token based algorithm yields low rejection rates over those with dedicated processor for task allocation.
{"title":"Dual-token-based fault-tolerant scheduling for hard real-time multiprocessor systems","authors":"Sungyoung Lee, S. Oh, Chul Hee Woo","doi":"10.1109/RTCSA.1998.726423","DOIUrl":"https://doi.org/10.1109/RTCSA.1998.726423","url":null,"abstract":"Real time multiprocessor systems frequently assume that there exists a dedicated processor for task allocation that never fails. This assumption is, however too strong in the sense that all the physical objects are subject to failure. Moreover once the dedicated processor fails, the whole multiprocessor system will fail. As a way to solve this problem, we propose a fault tolerant scheduling algorithm based on moving dual token. While the primary processor holding a primary token performs task allocation, the backup processor holding a backup token, in case the primary processor fails, does primary processor creation. Since no dedicated processor for task allocation exists in this scheme, failure of the whole multiprocessor system due to that of the dedicated processor can be avoided. In addition, the deadline friendly scheduling policy used for backup task allocation, compared to heuristic scheduling, allows easier implementation and improved scheduling predictability. Simulation results show that the proposed dual token based algorithm yields low rejection rates over those with dedicated processor for task allocation.","PeriodicalId":142319,"journal":{"name":"Proceedings Fifth International Conference on Real-Time Computing Systems and Applications (Cat. No.98EX236)","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117235944","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}
Pub Date : 1998-10-27DOI: 10.1109/RTCSA.1998.726350
L. Lundberg
Real-time systems often consist of a number of independent processes which operate under an age constraint. In such systems, the maximum time from the start of process L/sub i/ in cycle k to the end in cycle k+1 must not exceed the age constraint A/sub i/ for that process. Multiprocessors provide a scalable and cost-effective way of meeting the performance demands of such systems. The age constraint can be met using fixed priority scheduling and periods equal to A/sub i//2. However, this approach restricts the number of process sets which are schedulable. We define a method for obtaining process periods other than A/sub i//2. The periods are calculated in such a way that the age constraints are met. Our approach is better in the sense that a larger number of process sets can be scheduled compared to using periods equal to A/sub i//2.
{"title":"Multiprocessor scheduling of age constraint processes","authors":"L. Lundberg","doi":"10.1109/RTCSA.1998.726350","DOIUrl":"https://doi.org/10.1109/RTCSA.1998.726350","url":null,"abstract":"Real-time systems often consist of a number of independent processes which operate under an age constraint. In such systems, the maximum time from the start of process L/sub i/ in cycle k to the end in cycle k+1 must not exceed the age constraint A/sub i/ for that process. Multiprocessors provide a scalable and cost-effective way of meeting the performance demands of such systems. The age constraint can be met using fixed priority scheduling and periods equal to A/sub i//2. However, this approach restricts the number of process sets which are schedulable. We define a method for obtaining process periods other than A/sub i//2. The periods are calculated in such a way that the age constraints are met. Our approach is better in the sense that a larger number of process sets can be scheduled compared to using periods equal to A/sub i//2.","PeriodicalId":142319,"journal":{"name":"Proceedings Fifth International Conference on Real-Time Computing Systems and Applications (Cat. No.98EX236)","volume":"187 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133700579","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}
Pub Date : 1998-10-27DOI: 10.1109/RTCSA.1998.726348
Sung-Heun Oh, Seung-Min Yang
The Least-Laxity-First (LLF) scheduling algorithm assigns higher priority to a task with the least laxity, and has been proved to be optimal for uniprocessor systems. The algorithm, however is impractical to implement because laxity tie results in the frequent context switches among the tasks. The Modified Least-Laxity-First (MLLF) scheduling algorithm proposed in this paper solves the problem of the LLF scheduling algorithm by reducing the number of context switches significantly. By reducing the system overhead due to unnecessary context switches, the MLLF scheduling algorithm avoids the degradation of system performance and conserves more system resources for unanticipated aperiodic tasks. We propose the MLLF scheduling algorithm and prove its optimality. We show the performance enhancement of the proposed MLLF scheduling algorithm by using simulation results.
{"title":"A Modified Least-Laxity-First scheduling algorithm for real-time tasks","authors":"Sung-Heun Oh, Seung-Min Yang","doi":"10.1109/RTCSA.1998.726348","DOIUrl":"https://doi.org/10.1109/RTCSA.1998.726348","url":null,"abstract":"The Least-Laxity-First (LLF) scheduling algorithm assigns higher priority to a task with the least laxity, and has been proved to be optimal for uniprocessor systems. The algorithm, however is impractical to implement because laxity tie results in the frequent context switches among the tasks. The Modified Least-Laxity-First (MLLF) scheduling algorithm proposed in this paper solves the problem of the LLF scheduling algorithm by reducing the number of context switches significantly. By reducing the system overhead due to unnecessary context switches, the MLLF scheduling algorithm avoids the degradation of system performance and conserves more system resources for unanticipated aperiodic tasks. We propose the MLLF scheduling algorithm and prove its optimality. We show the performance enhancement of the proposed MLLF scheduling algorithm by using simulation results.","PeriodicalId":142319,"journal":{"name":"Proceedings Fifth International Conference on Real-Time Computing Systems and Applications (Cat. No.98EX236)","volume":"93 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116042573","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}
Pub Date : 1998-10-27DOI: 10.1109/RTCSA.1998.726347
Namyun Kim, Taewoong Kim, N. Chang, Heonshik Shin
This paper aims to enhance the response times of soft real-time end-to-end tasks while guaranteeing deadlines of hard real-time local tasks. Since the end-to-end task is comprised of multiple subtasks, we derive the intermediate timing attributes of subtasks taking into account precedence relations, and find the highest possible priorities of subtasks using the slack of hard real-time local tasks. The final result is a set of periodic tasks, which can be scheduled according to a fixed-priority scheme.
{"title":"Enhancing response times of end-to-end tasks using slack of local tasks","authors":"Namyun Kim, Taewoong Kim, N. Chang, Heonshik Shin","doi":"10.1109/RTCSA.1998.726347","DOIUrl":"https://doi.org/10.1109/RTCSA.1998.726347","url":null,"abstract":"This paper aims to enhance the response times of soft real-time end-to-end tasks while guaranteeing deadlines of hard real-time local tasks. Since the end-to-end task is comprised of multiple subtasks, we derive the intermediate timing attributes of subtasks taking into account precedence relations, and find the highest possible priorities of subtasks using the slack of hard real-time local tasks. The final result is a set of periodic tasks, which can be scheduled according to a fixed-priority scheme.","PeriodicalId":142319,"journal":{"name":"Proceedings Fifth International Conference on Real-Time Computing Systems and Applications (Cat. No.98EX236)","volume":"102 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122793676","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}
Pub Date : 1998-10-27DOI: 10.1109/RTCSA.1998.726421
Jai-hoon Kim, Kihyun Song, Kyunghee Choi, Gihyun Jung, Seunhun Jung
This paper presents an algorithm for scheduling imprecise tasks to minimize maximum error and analyzes its performance through intensive simulation. The imprecise computation is used to manage transient overload of computation. Each task for imprecise systems consists of a mandatory part and an optional part that can be skipped when systems are overloaded. The imprecise computation trades accuracy for meeting the deadline of tasks by skipping their optional parts. To increase accuracy for imprecise computation, we present a simple on-line scheduling algorithm that minimizes the maximum error. This algorithm executes mandatory parts of tasks first, then the optional parts in order to minimize maximum error. The proposed algorithm also increases schedulability by executing mandatory parts first. The proposed algorithm is simple and does not require any additional data structures such as the reservation list for maintaining mandatory parts.
{"title":"Performance evaluation of on-line scheduling algorithms for imprecise computation","authors":"Jai-hoon Kim, Kihyun Song, Kyunghee Choi, Gihyun Jung, Seunhun Jung","doi":"10.1109/RTCSA.1998.726421","DOIUrl":"https://doi.org/10.1109/RTCSA.1998.726421","url":null,"abstract":"This paper presents an algorithm for scheduling imprecise tasks to minimize maximum error and analyzes its performance through intensive simulation. The imprecise computation is used to manage transient overload of computation. Each task for imprecise systems consists of a mandatory part and an optional part that can be skipped when systems are overloaded. The imprecise computation trades accuracy for meeting the deadline of tasks by skipping their optional parts. To increase accuracy for imprecise computation, we present a simple on-line scheduling algorithm that minimizes the maximum error. This algorithm executes mandatory parts of tasks first, then the optional parts in order to minimize maximum error. The proposed algorithm also increases schedulability by executing mandatory parts first. The proposed algorithm is simple and does not require any additional data structures such as the reservation list for maintaining mandatory parts.","PeriodicalId":142319,"journal":{"name":"Proceedings Fifth International Conference on Real-Time Computing Systems and Applications (Cat. No.98EX236)","volume":"132 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128528673","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}
Pub Date : 1998-10-27DOI: 10.1109/RTCSA.1998.726349
Byung Kook Kim
A new task-scheduling algorithm with feedback latency is suggested for real-time control systems, which considers both point of views-control theoretic and real-time computing. Building a real-time control system has two steps in general. In the controller design stage, a control performance index is defined and a controller is designed which optimizes the given performance index while maintaining stability and rejecting disturbances. In the implementation stage, a set of controllers constitutes multiple control tasks, and scheduled to run on microprocessors, which should be schedulable with limited computing resources. The author reveals that the control performance depends not only on the control period but also on the feedback latency (latency from sensing, computation to actuation), which is revealed to have more impact. We formulate a new task-scheduling problem with a suitable control performance index including the feedback latency. An iterative search algorithm is suggested which is based on feedback latency computation method. An illustrative example demonstrated the applicability of the proposed method.
{"title":"Task scheduling with feedback latency for real-time control systems","authors":"Byung Kook Kim","doi":"10.1109/RTCSA.1998.726349","DOIUrl":"https://doi.org/10.1109/RTCSA.1998.726349","url":null,"abstract":"A new task-scheduling algorithm with feedback latency is suggested for real-time control systems, which considers both point of views-control theoretic and real-time computing. Building a real-time control system has two steps in general. In the controller design stage, a control performance index is defined and a controller is designed which optimizes the given performance index while maintaining stability and rejecting disturbances. In the implementation stage, a set of controllers constitutes multiple control tasks, and scheduled to run on microprocessors, which should be schedulable with limited computing resources. The author reveals that the control performance depends not only on the control period but also on the feedback latency (latency from sensing, computation to actuation), which is revealed to have more impact. We formulate a new task-scheduling problem with a suitable control performance index including the feedback latency. An iterative search algorithm is suggested which is based on feedback latency computation method. An illustrative example demonstrated the applicability of the proposed method.","PeriodicalId":142319,"journal":{"name":"Proceedings Fifth International Conference on Real-Time Computing Systems and Applications (Cat. No.98EX236)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130575695","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}
Pub Date : 1998-10-27DOI: 10.1109/RTCSA.1998.726351
Daoxu Chen, V. Lee, E. Chan
Timed token networks such as FDDI networks have been widely deployed to support real-time traffic such as voice and video communications. However the medium access control (MAC) protocol of FDDI allows transmission of synchronous messages up to at most one half of the total bandwidth of the network. Shin and Zheng (1995) have proposed a modification to the FDDI MAC protocol, called FDDI-M, which can double a ring's ability in supporting synchronous traffic. We compare the ability of FDDI-M to support synchronous traffic under different SBA schemes with that of FDDI. We first propose a new taxonomy of SBA schemes based on the underlying strategy used to partition the synchronous bandwidth. Next we present an analysis of the timing properties of the FDDI-M protocol, using the Worst Case Achievable Utilization (WCAU) as the performance metric. Our analytical results show that while FDDI-M improves the WCAU values under one class of SBA schemes, its performance under the other category of SBA schemes is mixed. We also perform extensive simulation to study performance of FDDI-M for MPEG video traffic, and conclude FDDI-M does outperform FDDI significantly at heavy load. The effect of SBA schemes under overload conditions is also shown to be relatively minor.
{"title":"On the ability of the FDDI-M protocol to support real-time traffic","authors":"Daoxu Chen, V. Lee, E. Chan","doi":"10.1109/RTCSA.1998.726351","DOIUrl":"https://doi.org/10.1109/RTCSA.1998.726351","url":null,"abstract":"Timed token networks such as FDDI networks have been widely deployed to support real-time traffic such as voice and video communications. However the medium access control (MAC) protocol of FDDI allows transmission of synchronous messages up to at most one half of the total bandwidth of the network. Shin and Zheng (1995) have proposed a modification to the FDDI MAC protocol, called FDDI-M, which can double a ring's ability in supporting synchronous traffic. We compare the ability of FDDI-M to support synchronous traffic under different SBA schemes with that of FDDI. We first propose a new taxonomy of SBA schemes based on the underlying strategy used to partition the synchronous bandwidth. Next we present an analysis of the timing properties of the FDDI-M protocol, using the Worst Case Achievable Utilization (WCAU) as the performance metric. Our analytical results show that while FDDI-M improves the WCAU values under one class of SBA schemes, its performance under the other category of SBA schemes is mixed. We also perform extensive simulation to study performance of FDDI-M for MPEG video traffic, and conclude FDDI-M does outperform FDDI significantly at heavy load. The effect of SBA schemes under overload conditions is also shown to be relatively minor.","PeriodicalId":142319,"journal":{"name":"Proceedings Fifth International Conference on Real-Time Computing Systems and Applications (Cat. No.98EX236)","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129630763","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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