| 1. |
- Amirijoo, Mehdi, 1978-, et al.
(author)
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Enhancing Feedback Control Scheduling Performance by On-line Quantification and Suppression of Measurement Disturbance
- 2005
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In: Proceedings of the 11th IEEE Real-Time and Embedded Technology and Applications Symposium. - 0769523021 ; , s. 2-11
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Conference paper (peer-reviewed)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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| 2. |
- Amirijoo, Mehdi, et al.
(author)
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Experimental Evaluation of Linear Time-Invariant Models for Feedback Performance Control in Real-Time Systems
- 2007
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In: Real-time systems. - : Springer Science+Business Media B.V.. - 0922-6443 .- 1573-1383. ; 35:3, s. 209-238
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Journal article (peer-reviewed)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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| 3. |
- Amirijoo, Mehdi, 1978-, et al.
(author)
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Finite Horizon QoS Prediction of Reconfigurable Firm Real-Time Systems
- 2006
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In: 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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Conference paper (peer-reviewed)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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| 4. |
- Amirijoo, Mehdi, et al.
(author)
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Generalized performance management of multi-class real-time imprecise data services
- 2005
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In: Real-Time Systems Symposium, 2005. RTSS 2005. 26th IEEE International. ; , s. 12-49
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Conference paper (other academic/artistic)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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| 5. |
- Amirijoo, Mehdi, 1978-, et al.
(author)
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QoD Adaptation for Achieving Lifetime Predictability of WSN Nodes Communicating over Satellite Links
- 2007
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In: International Conference on Networked Sensing Systems INSS,2007. - : IEEE. - 1424412315 ; , s. 19-26
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Conference paper (peer-reviewed)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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| 6. |
- Amirijoo, Mehdi, et al.
(author)
-
Quantifying and Suppressing the Measurement Disturbance in Feedback Controlled Real-Time Systems
- 2008
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In: Real-time systems. - : Springer. - 0922-6443 .- 1573-1383. ; 40:1, s. 44-76
-
Journal article (peer-reviewed)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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| 7. |
- Amirijoo, Mehdi, et al.
(author)
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Specification and Management of QoS in Real-Time Databases Supporting Imprecise Computations
- 2006
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In: IEEE Transactions on Computers. - 0018-9340 .- 1557-9956. ; 55:3, s. 304-319
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Journal article (peer-reviewed)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 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.
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| 8. |
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| 9. |
- Mathiason, Gunnar, et al.
(author)
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Virtual Full Replication by Adaptive Segmentation
- 2007
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In: 13th IEEE International Conference on Embedded and Real-Time Computing Systems and Applications (RTCSA 2007). - Los Alamitos, California, USA : IEEE. - 9780769529752 - 0769529755 ; , s. 327-337
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Conference paper (peer-reviewed)abstract
- We propose virtual full replication by adaptive segmentation (ViFuR-A), and evaluate its ability to maintain scalability in a replicated real-time database. With full replication and eventual consistency, transaction timeliness becomes independent of network delays for all transactions. However, full replication does not scale well, since all updates must be replicated to all nodes, also when data is needed only at a subset of the nodes. With virtual full replication that adapts to actual data needs, resource usage can be bounded and the database can be made scalable. We propose a scheme for adaptive segmentation that detects new data needs and adapts replication. The scheme includes an architecture, a scalable protocol and a replicated directory service that together maintains scalability. We show that adaptive segmentation bounds the required storage at a significantly lower level compared to static segmentation, for a typical workload where the data needs change repeatedly. Adaptation time can be kept constant for the workload when there are sufficient resources. Also, the storage is constant with an increasing amount of nodes and linear with an increasing rate of change to data needs.
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| 10. |
- Mathiason, Gunnar, et al.
(author)
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Virtual Full Replication for Scalable and Adaptive Real-Time Communication in Wireless Sensor Networks
- 2008
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In: Proceedings of the Second International Conference on Sensor Technologies and Applications (SENSORCOMM 2008). - Los Alamitos : IEEE. - 9780769533308 ; , s. 55-64
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Conference paper (peer-reviewed)abstract
- Sensor networks have limited resources and often support large-scale applications that need scalable propagation of sensor data to users. We propose a white-board style of communication in sensor networks using a distributed real-time database supporting Virtual Full Replication with Adaptive Segmentation. This allows mobile client nodes to access, transparently and efficiently, any sensor data at any node in the network. We present a two-tiered wireless architecture, and an adaptation protocol, for scalable and adaptive white-board communication in large-scale sensor networks. Sensor value readings at nodes of the sensor tier are published at nodes of the database tier as database updates to objects in a distributed real-time database. The search space of client nodes for sensor data is thus limited to the number of database nodes. With this scheme, we can show scalable resource usage and short adaptation times for several hundreds of database nodes and up to 50 moving clients.
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