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- 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, et al.
(författare)
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On Self-Optimization of the Random Access Procedure in 3G Long Term Evolution
- 2009
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Ingår i: Proceedings of the 11th IFIP/IEEE International Symposium on Integrated Network Management. - : IEEE. - 9781424439232 - 9781424439249
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Konferensbidrag (refereegranskat)abstract
- Operationally efficient radio networks typically feature a high degree of self-organization. This means less planning efforts and manual intervention, and a potential for better radio resource utilization when network elements adapts its operation to the observed local conditions. The focus in this paper is selfoptimization of the random access channel (RACH) in the 3G Long Term Evolution (LTE). A comprehensive tutorial about the RACH procedure is provided to span the complexity of the selfoptimization. Moreover, the paper addresses RACH key performance metrics and appropriate modeling of the various steps and components of the procedure. Finally, some coupling between parameters and key performance metrics as well as selfoptimization examples are presented together with a feasibility discussion. The main ambition with this workshop paper is to present and define a relevant set of self-optimization problems, rather than to provide a complete solution.
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| 9. |
- 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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| 10. |
- Amirijoo, Mehdi, 1978-
(författare)
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QoS Control of Real-Time Data Services under Uncertain Workload
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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