| 1. |
- Abdelzaher, T., et al.
(författare)
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The aperiodic multiprocessor utilization bound for liquid tasks
- 2002
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Ingår i: 8th IEEE Real-Time and Embedded Technology and Applications Symposium, 2002. Proceedings. - 1545-3421. - 0769517390 ; , s. 173-184
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Konferensbidrag (refereegranskat)abstract
- Real-time scheduling theory has developed powerful tools for translating conditions on aggregate system utilization into per-task schedulability guarantees. The main breakthrough has been Liu and Layland's utilization bound for schedulability of periodic tasks. In 2001 this bound was generalized by Abdelzaher and Lu to the aperiodic task case. In this paper we further generalize the aperiodic bound to the case of multiprocessors, and present key new insights into schedulability, analysis of aperiodic tasks. We consider a special task model, called the liquid task model, representative of high-performance servers with aperiodic workloads, such as network routers, web servers, proxies, and real-time databases. For this model, we derive the optimal multiprocessor utilization bound, defined on a utilization-like metric we call "synthetic utilization". This bound allows developing constant-time admission control tests that provide utilization-based absolute delay, tees. We show that the real utilization of admitted tasks can be close to unity even when synthetic utilization is kept below the bound. Thus, our results lead to multiprocessor systems which combine constant-time admission control with high utilization while making no periodicity assumptions regarding the task arrival pattern.
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| 2. |
- Henriksson, Dan, et al.
(författare)
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Feedback Scheduling of Model Predictive Controllers
- 2002
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Ingår i: Proceedings of the 8th IEEE Real-Time and Embedded Technology and Applications Symposium. - 0769517390 ; , s. 207-216
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Konferensbidrag (refereegranskat)abstract
- The paper presents some preliminaryresults on dynamic scheduling of model predictive controllers (MPCs).In an MPC, the control signal is obtained by on-line optimization of acost function, and the MPC task may experience very large variationsin execution time from sample to sample. Unique to this application,the cost function offers an explicit, on-line quality-of-servicemeasure for the task. Based on this insight, a feedback schedulingstrategy for multiple MPCs is proposed, where the scheduler allocatesCPU time to the tasks according to the current values of the costfunctions. Since the MPC algorithm is iterative, the feedbackscheduler may also abort a task prematurely to avoid excessiveinput-output latency. A case study is presented, where the newapproach is compared to conventional fixed-priority andearliest-deadline-first scheduling. General problems related to thereal-time implementation of MPCs are also discussed.
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| 3. |
- Uhlemann, Elisabeth, et al.
(författare)
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Concatenated hybrid ARQ - a flexible scheme for wireless real-time communication
- 2002
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Ingår i: Eighth IEEE Real-Time and Embedded Technology and Applications Symposium. - Los Alamitos, Calif. : IEEE Computer Society Press. - 0769517390 ; , s. 35-44
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Konferensbidrag (refereegranskat)abstract
- The concept of deadline dependent coding (DDC) has previously been suggested by the authors for maximizing the probability of delivering the required information before a given deadline in a wireless communication system.. In this paper, these principles are further developed using concatenated codes with iterative decoding, providing a new level of flexibility and robustness for DDC protocols. The strategy of DDC is to combine different coding and decoding methods with automatic repeat request (ARQ) techniques in order to fulfill the application requirements within a wireless realtime communication system. These requirements are formulated as two quality of service (QoS) parameters: deadline (tDL) and probability of correct delivery before the deadline (Pd), leading to a probabilistic view of realtime communication. An application can negotiate these QoS parameters with the DDC protocol, thus creating a flexible and fault-tolerant scheme.
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