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| 2. |
- Amirijoo, Mehdi, et al.
(författare)
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Algorithms for managing QoS for real-time data services using imprecise computation
- 2004
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Ingår i: Real-Time and Embedded Computing Systems and Applications 9th International Conference, RTCSA 2003, Tainan City, Taiwan, February 18-20, 2003. Revised Papers. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 3540219749 - 9783540219743 ; , s. 136-157
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Bokkapitel (refereegranskat)abstract
- Lately the demand for real-time data services has increased in applications where it is desirable to process user requests within their deadlines using fresh data. The real-time data services are usually provided by a real-time database (RTDB). Here, since the workload of the RTDBs cannot be precisely predicted, RTDBs can become overloaded. As a result, deadline misses and freshness violations may occur. To address this problem we propose a QoS-sensitive approach to guarantee a set of requirements on the behavior of RTDBs. Our approach is based on imprecise computation, applied on both data and transactions. We propose two algorithms to dynamically balance the workload and the quality of the data and transactions. Performance evaluations show that our algorithms give a robust and controlled behavior of RTDBs, in terms of transaction and data quality, even for transient overloads and with inaccurate run-time estimates of the transactions.
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| 3. |
- Amirijoo, Mehdi, 1978-, et al.
(författare)
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Enhancing Feedback Control Scheduling Performance by On-line Quantification and Suppression of Measurement Disturbance
- 2005
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Ingår i: Proceedings of the 11th IEEE Real-Time and Embedded Technology and Applications Symposium. - 0769523021 ; , s. 2-11
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Konferensbidrag (refereegranskat)abstract
- In the control of continuous and physical systems, the controlled system is sampled sufficiently fast to capture the system dynamics. 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 quantize the disturbance present in the measured variable as a function of the sampling period and we propose a measurement disturbance suppressive control structure. 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 and adaptation.
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| 4. |
- Amirijoo, Mehdi, 1978-, et al.
(författare)
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Error-Driven QoS Management in Imprecise Real-Time Databases
- 2003
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Ingår i: Euromicro Conference on Real-Time Systems,2003. - Los Alamitos, CA, USA : IEEE Computer Society. ; , s. 63-
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Konferensbidrag (refereegranskat)abstract
- In applications such as web-applications, e-commerce, and engine control, the demand for real-time data services has increased. In these applications, requests have to be processed within their deadlines using fresh data. Since the workload of these systems cannot be precisely predicted, they can become overloaded and as a result, deadline and freshness violations may occur. To address this problem we propose a QoS-sensitive approach based on imprecise computation, applied on transactions and data objects. We propose two algorithms FCS-HEF and FCS-HEDF that give a robust and controlled behavior of RTDBs in terms of transaction and data preciseness, even for transient overloads and with inaccurate run-time estimates of the transactions. Further, performance experiments show that the proposed algorithms outperform a set of baseline algorithms including FCS-EDF, which schedules the transactions using EDF.
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| 5. |
- Amirijoo, Mehdi, et al.
(författare)
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Experimental Evaluation of Linear Time-Invariant Models for Feedback Performance Control in Real-Time Systems
- 2007
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Ingår i: Real-time systems. - : Springer Science+Business Media B.V.. - 0922-6443 .- 1573-1383. ; 35:3, s. 209-238
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Amirijoo, Mehdi, 1978-, et al.
(författare)
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Finite Horizon QoS Prediction of Reconfigurable Firm Real-Time Systems
- 2006
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Ingår i: IEEE International Conference on Embedded and Real-Time Computing Systems and Applications,2006. - Los Alamitos, California, USA : IEEE Computer Society. ; , s. 233-
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Konferensbidrag (refereegranskat)abstract
- Updating real-time system software is often needed in response to errors and added requirements to the software. Stopping a running application, updating the software, and then restarting the application is not suitable for systems with high availability requirements. On the other hand, dynamically updating a system may increase the execution time of the tasks, thus, degrading the performance of the system. Degradation is not acceptable for performance-critical real-time systems as there are strict requirements on the performance. In this paper we present an approach that enables dynamic reconfiguration of a real-time system, where the performance of the system during a reconfiguration satisfies a given worst-case performance specification. Evaluation shows that the presented method is efficient in guaranteeing the worst-case performance of dynamically reconfigurable firm real-time systems.
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| 7. |
- Amirijoo, Mehdi, et al.
(författare)
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Generalized performance management of multi-class real-time imprecise data services
- 2005
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Ingår i: Real-Time Systems Symposium, 2005. RTSS 2005. 26th IEEE International. ; , s. 12-49
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 8. |
- Amirijoo, Mehdi, 1978-, et al.
(författare)
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QoD Adaptation for Achieving Lifetime Predictability of WSN Nodes Communicating over Satellite Links
- 2007
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Ingår i: International Conference on Networked Sensing Systems INSS,2007. - : IEEE. - 1424412315 ; , s. 19-26
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Konferensbidrag (refereegranskat)abstract
- In this paper we propose an architecture consisting of a particular type of node, namely a communication server that collects and aggregates data, and establishes a link between the users and the sensor nodes through satellite communication. A key challenge with satisfying a lifetime requirement of the communication server is the unpredictability of the sensor data volume arriving at the communication server and the transmission power of the satellite terminal. To provide lifetime predictability we propose an approach that automatically adjusts the quality of the data such that the specified lifetime if achieved. We have shown through an extensive evaluation that the approach manages to provide an actual lifetime within 2% of the specified lifetime despite variations in workload and communication link quality.
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| 9. |
- Amirijoo, Mehdi, et al.
(författare)
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Quantifying and Suppressing the Measurement Disturbance in Feedback Controlled Real-Time Systems
- 2008
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Ingår i: Real-time systems. - : Springer. - 0922-6443 .- 1573-1383. ; 40:1, s. 44-76
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Amirijoo, Mehdi, 1978-, et al.
(författare)
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Specification and Management of QoS in Imprecise Real-Time Databases
- 2003
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Ingår i: International Database Engineering and Applications Symposium,2003. - Los Alamitos, CA, USA : IEEE Computer Society. ; , s. 192-
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Konferensbidrag (refereegranskat)abstract
- 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. Since the workload of real-time databases RTDBs, providing real-time data services, cannot be precisely predicted, they can become overloaded and thereby cause temporal violations, resulting in a damage or even a catastrophe. Imprecise computation techniques address this problem and allow graceful degradation during overloads. In this paper, we present a framework consisting of a model for expressing QoS requirements in terms of data and transaction preciseness, 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 RTDBs, even for transient overloads and with inaccurate run-time estimates of the transactions. Further, performance experiments show that the proposed algorithms outperform a set of baseline algorithms, including FCS-EDF that schedules the transactions using EDF and feedback control.
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