Pub Date : 1998-06-17DOI: 10.1109/EMWRTS.1998.685068
S. Sáez, Joan Vila i Carbó, A. Crespo
The paper introduces improvements in partitioning schemes for multiprocessor real time systems which allow higher processor utilization and enhanced schedulability by using exact feasibility tests to evaluate the schedulability limit of a processor. The paper analyzes how to combine these tests with existing bin packing algorithms for processor allocation and provides new variants which are exhaustively evaluated using two assumptions: variable and fixed number of processors. The problem of evaluating these algorithms is complex, since metrics are usually based on comparing the performance of a given algorithm to an optimal one, but determining optimals is often NP hard on multiprocessors. This problem has been overcome by defining lower or upper bounds on the performance of an optimal algorithm and then defining metrics with respect these bounds. The evaluation has shown that the algorithms exhibit extremely good behavior and they can be considered very close to the maximum achievable utilization. It is also shown that dynamic priority policies produce significantly better results than fixed priority policies when task sets require high processor utilizations.
{"title":"Using exact feasibility tests for allocating real-time tasks in multiprocessor systems","authors":"S. Sáez, Joan Vila i Carbó, A. Crespo","doi":"10.1109/EMWRTS.1998.685068","DOIUrl":"https://doi.org/10.1109/EMWRTS.1998.685068","url":null,"abstract":"The paper introduces improvements in partitioning schemes for multiprocessor real time systems which allow higher processor utilization and enhanced schedulability by using exact feasibility tests to evaluate the schedulability limit of a processor. The paper analyzes how to combine these tests with existing bin packing algorithms for processor allocation and provides new variants which are exhaustively evaluated using two assumptions: variable and fixed number of processors. The problem of evaluating these algorithms is complex, since metrics are usually based on comparing the performance of a given algorithm to an optimal one, but determining optimals is often NP hard on multiprocessors. This problem has been overcome by defining lower or upper bounds on the performance of an optimal algorithm and then defining metrics with respect these bounds. The evaluation has shown that the algorithms exhibit extremely good behavior and they can be considered very close to the maximum achievable utilization. It is also shown that dynamic priority policies produce significantly better results than fixed priority policies when task sets require high processor utilizations.","PeriodicalId":318810,"journal":{"name":"Proceeding. 10th EUROMICRO Workshop on Real-Time Systems (Cat. No.98EX168)","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132822326","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 : 1998-06-17DOI: 10.1109/EMWRTS.1998.685071
E. Tovar, F. Vasques
The paper provides a comprehensive study on how to use Profibus networks to support real time communications, that is, ensuring the transmission of the real time messages before their deadlines. Profibus is based on a simplified Timed Token (TT) protocol, which is a well proved solution for real time communication systems. However, Profibus differences from the TT protocol prevent the application of the usual TT analysis. The main reason is that, conversely to the TT protocol, in the worst case, only one high priority message is processed per token visit. The major contribution of the paper is to prove that, despite this shortcoming, it is possible to guarantee communication real time behaviour with the Profibus protocol.
{"title":"Guaranteeing real-time message deadlines in PROFIBUS networks","authors":"E. Tovar, F. Vasques","doi":"10.1109/EMWRTS.1998.685071","DOIUrl":"https://doi.org/10.1109/EMWRTS.1998.685071","url":null,"abstract":"The paper provides a comprehensive study on how to use Profibus networks to support real time communications, that is, ensuring the transmission of the real time messages before their deadlines. Profibus is based on a simplified Timed Token (TT) protocol, which is a well proved solution for real time communication systems. However, Profibus differences from the TT protocol prevent the application of the usual TT analysis. The main reason is that, conversely to the TT protocol, in the worst case, only one high priority message is processed per token visit. The major contribution of the paper is to prove that, despite this shortcoming, it is possible to guarantee communication real time behaviour with the Profibus protocol.","PeriodicalId":318810,"journal":{"name":"Proceeding. 10th EUROMICRO Workshop on Real-Time Systems (Cat. No.98EX168)","volume":"143 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121785727","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 : 1998-06-17DOI: 10.1109/EMWRTS.1998.685074
I. Bate, A. Burns
The paper describes work carried out to reduce the pessimism in distributed systems timing analysis. The starting point for the paper is the need to prove that the timing properties of a system are met in an efficient and effective manner. The paper shows that an exact approach to the analysis can be intractable, and other approaches are too pessimistic. Using extensive simulation, based on realistic requirements from the domain of interest, a new approach to distributed timing analysis is developed using an integrated approach to task attribute assignment and timing analysis. The new approach is up to 20% more effective than previous tractable approaches. An additional benefit is the approach has a greater resilience to change than the other approaches considered. The results contained within the paper demonstrate the effectiveness of our approach.
{"title":"Investigation of the pessimism in distributed systems timing analysis","authors":"I. Bate, A. Burns","doi":"10.1109/EMWRTS.1998.685074","DOIUrl":"https://doi.org/10.1109/EMWRTS.1998.685074","url":null,"abstract":"The paper describes work carried out to reduce the pessimism in distributed systems timing analysis. The starting point for the paper is the need to prove that the timing properties of a system are met in an efficient and effective manner. The paper shows that an exact approach to the analysis can be intractable, and other approaches are too pessimistic. Using extensive simulation, based on realistic requirements from the domain of interest, a new approach to distributed timing analysis is developed using an integrated approach to task attribute assignment and timing analysis. The new approach is up to 20% more effective than previous tractable approaches. An additional benefit is the approach has a greater resilience to change than the other approaches considered. The results contained within the paper demonstrate the effectiveness of our approach.","PeriodicalId":318810,"journal":{"name":"Proceeding. 10th EUROMICRO Workshop on Real-Time Systems (Cat. No.98EX168)","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116003861","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 : 1998-06-17DOI: 10.1109/EMWRTS.1998.685087
V. Lee, K. Lam, Nelson Wai-Hung Tsang
The use of portable computers with a wireless connection to distributed databases will become as popular as the use of mobile phones in the near future. The rapidly advancing technology in this area has initiated new research areas and challenging research questions. One new area is the support of real-time database systems with a wireless network. The authors have built a model with sufficient details of a wireless distributed real-time database system (WDRTDBS) and have performed simulation experiments to identify the effect of wireless bandwidth, which is one of the most scarce resources in a wireless environment, on the performance of distributed real-time database systems. Through the experiments, they are trying to figure out the criterion for building efficient wireless DRTDBS in terms of performance. The simulation results reveal that the call duration, which may lead to call blocking and prolonged call waiting, impacts on the performance of the DRTDBS in terms of resource contention and transaction deadline missing.
{"title":"Transaction processing in wireless distributed real-time databases","authors":"V. Lee, K. Lam, Nelson Wai-Hung Tsang","doi":"10.1109/EMWRTS.1998.685087","DOIUrl":"https://doi.org/10.1109/EMWRTS.1998.685087","url":null,"abstract":"The use of portable computers with a wireless connection to distributed databases will become as popular as the use of mobile phones in the near future. The rapidly advancing technology in this area has initiated new research areas and challenging research questions. One new area is the support of real-time database systems with a wireless network. The authors have built a model with sufficient details of a wireless distributed real-time database system (WDRTDBS) and have performed simulation experiments to identify the effect of wireless bandwidth, which is one of the most scarce resources in a wireless environment, on the performance of distributed real-time database systems. Through the experiments, they are trying to figure out the criterion for building efficient wireless DRTDBS in terms of performance. The simulation results reveal that the call duration, which may lead to call blocking and prolonged call waiting, impacts on the performance of the DRTDBS in terms of resource contention and transaction deadline missing.","PeriodicalId":318810,"journal":{"name":"Proceeding. 10th EUROMICRO Workshop on Real-Time Systems (Cat. No.98EX168)","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131179051","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 : 1998-06-17DOI: 10.1109/EMWRTS.1998.684942
Tei-Wei Kuo, Wang Yang, Kwei-Jay Lin
A class of real time scheduling algorithms EGPS is proposed. Using EGPS, the schedulability of each process is enforced by a guaranteed CPU service rate, independent of the demands of other processes. Our research uses a GPS based framework for periodic and sporadic process scheduling, jitter control, service rate adjustment, and mixed scheduling of soft and hard real time processes. We then study the performance of the proposed algorithms by using a generic avionics platform example for our simulation experiments in jitter control and mixed scheduling of soft and hard real time processes.
{"title":"EGPS: a class of real-time scheduling algorithms based on processor sharing","authors":"Tei-Wei Kuo, Wang Yang, Kwei-Jay Lin","doi":"10.1109/EMWRTS.1998.684942","DOIUrl":"https://doi.org/10.1109/EMWRTS.1998.684942","url":null,"abstract":"A class of real time scheduling algorithms EGPS is proposed. Using EGPS, the schedulability of each process is enforced by a guaranteed CPU service rate, independent of the demands of other processes. Our research uses a GPS based framework for periodic and sporadic process scheduling, jitter control, service rate adjustment, and mixed scheduling of soft and hard real time processes. We then study the performance of the proposed algorithms by using a generic avionics platform example for our simulation experiments in jitter control and mixed scheduling of soft and hard real time processes.","PeriodicalId":318810,"journal":{"name":"Proceeding. 10th EUROMICRO Workshop on Real-Time Systems (Cat. No.98EX168)","volume":"43 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121586278","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 : 1998-06-17DOI: 10.1109/EMWRTS.1998.685084
Sylvain Lauzac, R. Melhem, D. Mossé
The authors study GRMS, a global scheduling scheme for rate monotonic tasks on a multiprocessor. Several admission control algorithms for GRMS are presented, both for hard and soft real-time tasks. The average performance of these admission control algorithms is compared with the performance of known partitioning schemes. The result of these comparisons outlines some situations where one scheme is preferable over the other. Partitioning schemes are better suited for hard real-time systems, while a global scheme is preferable for soft real-time systems.
{"title":"Comparison of global and partitioning schemes for scheduling rate monotonic tasks on a multiprocessor","authors":"Sylvain Lauzac, R. Melhem, D. Mossé","doi":"10.1109/EMWRTS.1998.685084","DOIUrl":"https://doi.org/10.1109/EMWRTS.1998.685084","url":null,"abstract":"The authors study GRMS, a global scheduling scheme for rate monotonic tasks on a multiprocessor. Several admission control algorithms for GRMS are presented, both for hard and soft real-time tasks. The average performance of these admission control algorithms is compared with the performance of known partitioning schemes. The result of these comparisons outlines some situations where one scheme is preferable over the other. Partitioning schemes are better suited for hard real-time systems, while a global scheme is preferable for soft real-time systems.","PeriodicalId":318810,"journal":{"name":"Proceeding. 10th EUROMICRO Workshop on Real-Time Systems (Cat. No.98EX168)","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116010793","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 : 1998-06-17DOI: 10.1109/EMWRTS.1998.685127
T. Savor, R. Seviora
The functionality of many real-time systems depends critically on their software. It is important to know whether their software operates correctly or whether failures are occurring. This would help system operators take corrective actions before minor problems escalate into major disruptions. The paper considers one approach to automatic detection of software failures called supervision. In this approach, a separate unit called the supervisor observes the inputs and outputs of the target program. The supervisor knows what the intended behavior of the target program is and reports deviations as failures. The focus is on event-driven, embedded real-time software. The paper first overviews major issues involved in supervision. These include the definition of correct behavior, observability of program inputs and outputs, dealing with specification nondeterminism, tradeoffs between failure detection accuracy and computational cost, and the continuation of supervision after occurrences of failures. The paper then summarizes experience obtained in supervision of a control program of a small telephone exchange. The exchange and its telephones were simulated on a multiprocessor workstation. The summary includes the results obtained for failure detection capability and computational cost.
{"title":"Automatic detection of software failures: issues and experience","authors":"T. Savor, R. Seviora","doi":"10.1109/EMWRTS.1998.685127","DOIUrl":"https://doi.org/10.1109/EMWRTS.1998.685127","url":null,"abstract":"The functionality of many real-time systems depends critically on their software. It is important to know whether their software operates correctly or whether failures are occurring. This would help system operators take corrective actions before minor problems escalate into major disruptions. The paper considers one approach to automatic detection of software failures called supervision. In this approach, a separate unit called the supervisor observes the inputs and outputs of the target program. The supervisor knows what the intended behavior of the target program is and reports deviations as failures. The focus is on event-driven, embedded real-time software. The paper first overviews major issues involved in supervision. These include the definition of correct behavior, observability of program inputs and outputs, dealing with specification nondeterminism, tradeoffs between failure detection accuracy and computational cost, and the continuation of supervision after occurrences of failures. The paper then summarizes experience obtained in supervision of a control program of a small telephone exchange. The exchange and its telephones were simulated on a multiprocessor workstation. The summary includes the results obtained for failure detection capability and computational cost.","PeriodicalId":318810,"journal":{"name":"Proceeding. 10th EUROMICRO Workshop on Real-Time Systems (Cat. No.98EX168)","volume":"74 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127355032","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 : 1998-06-17DOI: 10.1109/EMWRTS.1998.685081
M. Natale, A. Meschi
The paper presents a scheme for guaranteeing the scheduling of real-time computations in a distributed environment. The authors propose a process model where only true (local or end-to-end) deadlines need to be specified. They assume all local interactions among processes are based on shared memory communication, protected by priority ceiling semaphores. Remote interactions are client-server blocking communications. The result is both a scheduling policy and a methodology to guarantee the integrated scheduling of processes and network messages. Both processes and messages are scheduled according to a fixed-priority scheme that can easily be implemented on most operating systems and a few network protocols. The procedure that checks the schedulability of the distributed computation against end-to-end deadlines is simple enough to be proposed as a scheme for a dynamic guarantee.
{"title":"Guaranteeing end-to-end deadlines in distributed client-server applications","authors":"M. Natale, A. Meschi","doi":"10.1109/EMWRTS.1998.685081","DOIUrl":"https://doi.org/10.1109/EMWRTS.1998.685081","url":null,"abstract":"The paper presents a scheme for guaranteeing the scheduling of real-time computations in a distributed environment. The authors propose a process model where only true (local or end-to-end) deadlines need to be specified. They assume all local interactions among processes are based on shared memory communication, protected by priority ceiling semaphores. Remote interactions are client-server blocking communications. The result is both a scheduling policy and a methodology to guarantee the integrated scheduling of processes and network messages. Both processes and messages are scheduled according to a fixed-priority scheme that can easily be implemented on most operating systems and a few network protocols. The procedure that checks the schedulability of the distributed computation against end-to-end deadlines is simple enough to be proposed as a scheme for a dynamic guarantee.","PeriodicalId":318810,"journal":{"name":"Proceeding. 10th EUROMICRO Workshop on Real-Time Systems (Cat. No.98EX168)","volume":"73 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126845359","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 : 1998-06-17DOI: 10.1109/EMWRTS.1998.685085
M. Bodlaender, P. V. D. Stok
The authors propose database support for large sets of temporal, real-time data. Prediction models are supported: transactions can write data items to the database that have been "measured in the future". Therefore, it is necessary to allow multiple instances of the same data item, with different times of measurement. This requires larger storage requirements, but can also be used for interpolation of intermediate values, and extrapolation of future values. It is recognized that temporal correctness of data is a characteristic of the usage of the data item. Real-time data requirements are specified for each individual transaction, rather than for each data item. Transactions can access multiple instances of the same data item (for extrapolation purposes), and can specify separate temporal constraints for each accessed instance. An implementation of a hard-real-time database that realizes these requirements is given, to show that the specified requirements are realistic.
{"title":"A transaction-based temporal data model that supports prediction in real-time databases","authors":"M. Bodlaender, P. V. D. Stok","doi":"10.1109/EMWRTS.1998.685085","DOIUrl":"https://doi.org/10.1109/EMWRTS.1998.685085","url":null,"abstract":"The authors propose database support for large sets of temporal, real-time data. Prediction models are supported: transactions can write data items to the database that have been \"measured in the future\". Therefore, it is necessary to allow multiple instances of the same data item, with different times of measurement. This requires larger storage requirements, but can also be used for interpolation of intermediate values, and extrapolation of future values. It is recognized that temporal correctness of data is a characteristic of the usage of the data item. Real-time data requirements are specified for each individual transaction, rather than for each data item. Transactions can access multiple instances of the same data item (for extrapolation purposes), and can specify separate temporal constraints for each accessed instance. An implementation of a hard-real-time database that realizes these requirements is given, to show that the specified requirements are realistic.","PeriodicalId":318810,"journal":{"name":"Proceeding. 10th EUROMICRO Workshop on Real-Time Systems (Cat. No.98EX168)","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121551015","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 : 1998-06-17DOI: 10.1109/EMWRTS.1998.685067
Taewoong Kim, Heonshik Shin, N. Chang
The paper addresses the problem of scheduling periodic messages in demand priority network standardized by IEEE 802.12 Committee. As regards the real time property of the demand priority network, unnecessary blocking time due to its round robin based MAC protocol may cause periodic messages to miss their hard deadlines and result in low schedulability of periodic messages. We propose a new message scheduling algorithm to enforce a priority based preemptive message transmission on the frame basis. Before a node transmits a periodic message, it broadcasts the priority of message for all nodes to construct a network wide ready queue in order of priority. A node can transmit a periodic message only when its message is at the head of the ready queue. We have derived sufficient and necessary conditions for both static and dynamic priority assignment in order to determine the schedulability of periodic messages. The simulation study shows that the proposed algorithm significantly improves the guarantee ratio of periodic messages.
{"title":"Scheduling algorithm for hard real-time communication in demand priority network","authors":"Taewoong Kim, Heonshik Shin, N. Chang","doi":"10.1109/EMWRTS.1998.685067","DOIUrl":"https://doi.org/10.1109/EMWRTS.1998.685067","url":null,"abstract":"The paper addresses the problem of scheduling periodic messages in demand priority network standardized by IEEE 802.12 Committee. As regards the real time property of the demand priority network, unnecessary blocking time due to its round robin based MAC protocol may cause periodic messages to miss their hard deadlines and result in low schedulability of periodic messages. We propose a new message scheduling algorithm to enforce a priority based preemptive message transmission on the frame basis. Before a node transmits a periodic message, it broadcasts the priority of message for all nodes to construct a network wide ready queue in order of priority. A node can transmit a periodic message only when its message is at the head of the ready queue. We have derived sufficient and necessary conditions for both static and dynamic priority assignment in order to determine the schedulability of periodic messages. The simulation study shows that the proposed algorithm significantly improves the guarantee ratio of periodic messages.","PeriodicalId":318810,"journal":{"name":"Proceeding. 10th EUROMICRO Workshop on Real-Time Systems (Cat. No.98EX168)","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1998-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115234529","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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