cs6235-3A-abdel-talk

cs6235-3A-abdel-talk - 9/27/2010 1 CS4220 Embedded Systems...

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9/27/2010 1 CS4220 Embedded Systems CS6235 Real CS6235 Real-Time Systems Time Systems 3A: Feedback Control of QoS Instructor: Calton Pu calton.pu@cc TAs: Qinyi Wu (qxw@cc) Peter Budny (peterb@cc) Feedback Control of QoS Tarek Abdelzaher Department of Computer Science University of Virginia
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9/27/2010 2 The Web QoS Group Group is formed in 1999 Projects: Web performance Deeply embedded sensor networks Real-time systems Students Ying Lu, Chenyang Lu, Sagnik Bhattacharya, Seejo Sebastine Performance Control in Server End systems How to design adaptive services which meet pre-specified performance requirements? How to model the effects of feedback (adaptation) in software architectures for QoS guarantees? How to use software feedback to achieve performance requirements?
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9/27/2010 3 Observation Physical and engineering sciences have a well developed analytic foundation for performance control in physical systems No such unified foundation exists for performance control of software services The objective of this research effort is to establish such a foundation based on control theory and scheduling theory Why Control Theory? Successful track record in physical process control Performance guarantees in the face of uncertainty, non-linearities, time-variations, etc. Does not require accurate system models Utilizes feedback to improve performance Performance of software services is governed by queuing dynamics which may be expressed by differential equations akin to those of physical systems
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9/27/2010 4 Feedback Control Versus Queuing Theory Queuing theory Off-line predictive analysis Assumptions about the arrival process Difficult to analyze some distributions Control-theory On-line input/output difference equations No assumptions about the arrival process Utilize run-time feedback for error correction Feedback Control Versus Optimization Optimization Works better if the performance problem is formulated as one of maximizing or minimizing some metric Control-theory Works well if the performance problem is one of maintaining an invariant, or is a tradeoff between two conflicting metrics
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9/27/2010 5 Software Performance Control Control theory: Robust guarantees on aggregate state and global performance metrics (e.g., average delay, total utilization, etc) Scheduling theory: Guarantees on “microscopic” performance metrics (e.g., individual response times) Conditions on aggregate state Theoretical Elements of a QoS Control Methodology Computing Tasks Resource Scheduling Resource Queues Modeling Difference Equation Models Feedback Control Desired Performance Fine-grained Performance Guarantees Scheduling Theory
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cs6235-3A-abdel-talk - 9/27/2010 1 CS4220 Embedded Systems...

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