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QoS Control of Real-Time Data Services under Uncertain Workload
Linköping University, Department of Computer and Information Science, RTSLAB - Real-Time Systems Laboratory. Linköping University, The Institute of Technology.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Real-time systems comprise computers that must generate correct results in a timely manner. This involves a wide spectrum of computing systems found in our everyday life ranging from computers in rockets to our mobile phones. The criticality of producing timely results defines the different types of realtime systems. On one hand, we have the so-called hard real-time systems, where failing to meet deadlines may result in a catastrophe. In this thesis we are, however, concerned with firm and soft real-time systems, where missing deadlines is acceptable at the expense of degraded system performance. The usage of firm and soft real-time systems has increased rapidly during the last years, mainly due to the advent of applications in multimedia, telecommunication, and e-commerce. These systems are typically data-intensive, with the data normally spanning from low-level control data, typically acquired from sensors, to high-level management and business data. In contrast to hard real-time systems, the environments in which firm and soft real-time systems operate in are typically open and highly unpredictable. For example, the workload applied on a web server or base station in telecommunication systems varies according to the needs of the users, which is hard to foresee. In this thesis we are concerned with quality of service (QoS) management of data services for firm and soft real-time systems. The approaches and solutions presented aim at providing a general understanding of how the QoS can be guaranteed according to a given specification, even if the workload varies unpredictably. The QoS specification determines the desired QoS during normal system operation, and the worst-case system performance and convergence rate toward the desired setting in the face of transient overloads. Feedback control theory is used to control QoS since little is known about the workload applied on the system. Using feedback control the difference between the measured QoS and the desired QoS is formed and fed into a controller, which computes a change to the operation of the real-time system. Experimental evaluation shows that using feedback control is highly effective in managing QoS such that a given QoS specification is satisfied. This is a key step toward automatic management of intricate systems providing real-time data services.

Place, publisher, year, edition, pages
Institutionen för datavetenskap , 2007. , 244 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1143
Keyword [en]
real-time system, database, feedback control
National Category
Computer Science
Identifiers
URN: urn:nbn:se:liu:diva-10016ISBN: 978-91-85895-49-6 (print)OAI: oai:DiVA.org:liu-10016DiVA: diva2:16753
Public defence
2007-11-15, Planck, Fysikhuset, Linköpings universitet, 13:15 (English)
Opponent
Supervisors
Available from: 2007-10-17 Created: 2007-10-17 Last updated: 2009-04-22
List of papers
1. Specification and Management of QoS in Real-Time Databases Supporting Imprecise Computations
Open this publication in new window or tab >>Specification and Management of QoS in Real-Time Databases Supporting Imprecise Computations
2006 (English)In: IEEE Transactions on Computers, ISSN 0018-9340, Vol. 55, no 3, 304 - 319 p.Article in journal (Refereed) Published
Abstract [en]

Real-time applications such as e-commerce, flight control, chemical and nuclear control, and telecommunication are becoming increasingly sophisticated in their data needs, resulting in greater demands for real-time data services that are provided by real-time databases. Since the workload of real-time databases cannot be precisely predicted, they can become overloaded and thereby cause temporal violations, resulting in damage or even a catastrophe. Imprecise computation techniques address this problem and allow graceful degradation during overloads. In this paper, we present a framework for QoS specification and management consisting of a model for expressing QoS requirements, an architecture based on feedback control scheduling, and a set of algorithms implementing different policies and behaviors. Our approach gives a robust and controlled behavior of real-time databases, even for transient overloads and with inaccurate runtime estimates of the transactions. Further, performance experiments show that the proposed algorithms outperform a set of baseline algorithms that uses feedback control.

Keyword
Real-time and embedded systems, real-time data services, imprecise computation, feedback control, modeling techniques
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-12635 (URN)10.1109/TC.2006.45 (DOI)
Available from: 2007-10-17 Created: 2007-10-17 Last updated: 2009-02-10
2. Experimental Evaluation of Linear Time-Invariant Models for Feedback Performance Control in Real-Time Systems
Open this publication in new window or tab >>Experimental Evaluation of Linear Time-Invariant Models for Feedback Performance Control in Real-Time Systems
2007 (English)In: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 35, no 3, 209-238 p.Article in journal (Refereed) Published
Abstract [en]

In recent years a new class of soft real-time applications operating in unpredictable environments has emerged. Typical for these applications is that neither the resource requirements nor the arrival rates of service requests are known or available a priori. It has been shown that feedback control is very effective to support the specified performance of dynamic systems that are both resource insufficient and exhibit unpredictable workloads. To efficiently use feedback control scheduling it is necessary to have a model that adequately describes the behavior of the system. In this paper we experimentally evaluate the accuracy of four linear time-invariant models used in the design of feedback controllers. We introduce a model (DYN) that captures additional system dynamics, which a previously published model (STA) fails to include. The accuracy of the models are evaluated by validating the models with regard to measured data from the controlled system and through a set of experiments where we evaluate the performance of a set of feedback control schedulers tuned using these models. From our evaluations we conclude that second order models (e.g., DYN) are more accurate than first order models (e.g. STA). Further we show that controllers tuned using second order models perform better than controllers tuned using first order models.

Place, publisher, year, edition, pages
Springer Science+Business Media B.V., 2007
Keyword
Feedback control scheduling, Modeling, Model validation, System identification
National Category
Control Engineering
Identifiers
urn:nbn:se:liu:diva-12636 (URN)10.1007/s11241-006-9008-8 (DOI)
Available from: 2007-10-17 Created: 2007-10-17 Last updated: 2017-12-14
3. Robust Quality Management for Differentiated Imprecise Data Services
Open this publication in new window or tab >>Robust Quality Management for Differentiated Imprecise Data Services
2004 (English)In: Proceedings of the 25th IEEE International Real-Time Systems Symposium, 2004, 265-275 p.Conference paper, Published paper (Refereed)
Abstract [en]

Several applications, such as Web services and e-commerce, are operating in open environments where the workload characteristics, such as the load applied on the system and the worst-case execution times, are inaccurate or even not known in advance. This implies that transactions submitted to a real-time database cannot be subject to exact schedulability analysis given the lack of a priori knowledge of the workload. In this paper we propose an approach, based on feedback control, for managing the quality of service of real-time databases that provide imprecise and differentiated services, given inaccurate workload characteristics. For each service class, the database operator specifies the quality of service requirements by explicitly declaring the precision requirements of the data and the results of the transactions. The performance evaluation shows that our approach provides reliable quality of service even in the face of varying load and inaccurate execution time estimates.

Keyword
Real-time systems, Real-time databases, Control theory, Realtidssystem, Realtidsdatabaser, Reglerteknik, CUGS
National Category
Control Engineering
Identifiers
urn:nbn:se:liu:diva-12637 (URN)10.1109/REAL.2004.49 (DOI)0-7695-2247-5 (ISBN)
Conference
25th IEEE International Real-Time Systems Symposium, Lisbon, Portugal, December 5-8, 2004
Available from: 2007-10-17 Created: 2007-10-17 Last updated: 2013-07-04
4. Generalized performance management of multi-class real-time imprecise data services
Open this publication in new window or tab >>Generalized performance management of multi-class real-time imprecise data services
Show others...
2005 (English)In: Real-Time Systems Symposium, 2005. RTSS 2005. 26th IEEE International, 2005, 12-49 p.Conference paper, Published paper (Other academic)
Abstract [en]

The intricacy of real-time data service management increases mainly due to the emergence of applications operating in open and unpredictable environments, increases in software complexity, and need for performance guarantees. In this paper we propose an approach for managing the quality of service of real-time databases that provide imprecise and differentiated services, and that operate in unpredictable environments. Transactions are classified into service classes according to their level of importance. Transactions within each service class are further classified into subclasses based on their quality of service requirements. In this way transactions are explicitly differentiated according to their importance and quality of service requests. The performance evaluation shows that during overloads the most important transactions are guaranteed to meet their deadlines and that reliable quality of service is provided even in the face of varying load and execution time estimation errors.

Keyword
real-time system, database, QoS, feedback control
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-12638 (URN)10.1109/RTSS.2005.23 (DOI)
Available from: 2007-10-17 Created: 2007-10-17 Last updated: 2009-04-22
5. Quantifying and Suppressing the Measurement Disturbance in Feedback Controlled Real-Time Systems
Open this publication in new window or tab >>Quantifying and Suppressing the Measurement Disturbance in Feedback Controlled Real-Time Systems
2008 (English)In: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 40, no 1, 44-76 p.Article in journal (Refereed) Published
Abstract [en]

In the control of continuous and physical systems, the controlled system is sampled sufficiently fast to capture the dynamics of the system. In general, this property cannot be applied to the control of computer systems as the measured variables are often computed over a data set, e.g., deadline miss ratio. In this paper we quantify the disturbance present in the measured variable as a function of the data set size and the sampling period, and we propose a feedback control structure that suppresses the measurement disturbance. The experiments we have carried out show that a controller using the proposed control structure outperforms a traditional control structure with regard to performance reliability.

Place, publisher, year, edition, pages
Springer, 2008
Keyword
Adaptive scheduling, Feedback control, Measurement disturbance, System disturbance
National Category
Control Engineering
Identifiers
urn:nbn:se:liu:diva-12639 (URN)10.1007/s11241-008-9048-3 (DOI)
Available from: 2007-10-17 Created: 2007-10-17 Last updated: 2017-12-14

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Amirijoo, Mehdi

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