This paper presents a feedback control real-time scheduling (FCS) framework for adaptive real-time systems. An advantage of the FCS framework is its use of feedback control theory (rather than ad hoc solutions) as a scientific underpinning. We apply a control theory based methodology to systematically design FCS algorithms to satisfy the transient and steady state performance specifications of real-time systems. In particular, we establish dynamic models of real-time systems and develop performance analyses of FCS algorithms, which are major challenges and key steps for the design of control theory based adaptive real-time systems. We also present a FCS architecture that allows plug-ins of different real-time scheduling policies and QoS optimization algorithms. Based on our framework, we identify different categories of real-time applications where different FCS algorithms should be applied. Performance evaluation results demonstrate that our analytically tuned FCS algorithms provide robust transient and steady state performance guarantees for periodic and aperiodic tasks even when the task execution times vary by as much as 100% from the initial estimate.

This paper presents the design, implementation, and evaluation of an adaptive architecture to provide relative delay guarantees for different service classes on web servers under HTTP 1.1. The first contribution of this paper is the architecture based on a feedback control loop that enforces desired relative delays among classes via dynamic connection scheduling and process reallocation. The second contribution is our use of feedback control theory to design the feedback loop with proven performance guarantees. In contrast with ad hoc approaches that often rely on laborious tuning and design iterations, our control theory approach enables us to systematically design an adaptive web server with established analytical methods. The design methodology includes using system identification to establish a dynamic model, and using the Root Locus method to design a feedback controller to satisfy performance specifications of a web server. The adaptive architecture has been implemented by modifying an Apache web server. Experimental results demonstrate that our adaptive server achieves robust relative delay guarantees even when workload varies significantly. Properties of our adaptive web server include guaranteed stability, and satisfactory efficiency and accuracy in achieving the desired relative delay differentiation. 1.

While early research on real-time computing was concerned with guaranteeing avoidance of undesirable effects' such as overload and deadline misses, adaptive real-time systems are designed to handle such effects' dynamically. Various research efforts' have addressed the characterization and improvement of the dynamic behavior of real-time systems. However, to the authors" knowledge, no unified framework exists' for designing adaptive, real-time software systems based on specifications of desired dynamic behavior. We propose such a framework based on control theory. Using control theory a designer can (i) specify the desired behavior in terms of a set of performance metrics' that can be mapped to a dynamic response of the control system, (ii) establish an underlying control model of the real-time systems, and (iii) design a resource scheduler using feedback control design methods to guarantee runtime satisfaction of the specs. This is in contrast to more ad hoc techniques. We also show that simply using long term average performance metrics is not sufficient in designing controllers. We then develop a new algorithm based on two PID controllers' that meet both the transient and steady state performance requirements.

This paper describes the design and implementation of a real-time, streaming, Internet video and audio player. The player has a number of advanced features including dynamic adaptation to changes in available bandwidth, latency and latency variation; a multi-dimensional media scaling capability driven by user-specified quality of service (QoS) requirements; and support for complex content comprising multiple synchronized video and audio streams. The player was developed as part of the QUASAR + project at Oregon Graduate Institute, is freely available, and serves as a testbed for research in adaptive resource management and QoS control. Keywords: Internet, video, real-time, MPEG, adaptive, feedback, quality of service 1. INTRODUCTION Digital multimedia systems are becoming ubiquitous, with nearly all computer platforms offering support for realtime datatypes such as audio and video. There has also been a rapid proliferation of communications networks, giving multimedia computing th...

This paper presents the design and implementation of an adaptive architecture to provide relative, absolute and hybrid service delay guarantees for different service classes on web servers under HTTP 1.1. The first contribution of this paper is the architecture based on feedback control loops that enforce delay guarantees for classes via dynamic connection scheduling and process reallocation. The second contribution is our use of feedback control theory to design the feedback loop with proven performance guarantees. In contrast with ad hoc approaches that often rely on laborious tuning and design iterations, our control theory approach enables us to systematically design an adaptive web server with established analytical methods. The design methodology includes using system identification to establish dynamic models for a web server, and using the Root Locus method to design feedback controllers to satisfy performance specifications. The adaptive architecture has been implemented by modifying an Apache web server. Experimental results demonstrate that our adaptive server provides robust delay guarantees even when workload varies significantly. Properties of our adaptive web server also include guaranteed stability, and satisfactory efficiency and accuracy in achieving desired delay or delay differentiation. 1.

The emergence of streaming multimedia players provides users with low latency audio and video content over the Internet. Providing high-quality, best e ort, real-time multimedia content requires adaptive delivery schemes that fairly share the available network bandwidth with reliable data protocols. Real-time multimedia tra c must avoid halting TCP-based HTTP tra c! This paper proposes a new ow and congestion control scheme, SCP (Streaming Control Protocol), for realtime streaming of continuous multimedia data across the Internet. The design of SCP arose from our long-time experience in building and using an adaptive real-time streaming video player. SCP addresses two issues associated with real-time streaming. First, it uses a congestion control policy that allows it to fairly share network bandwidth with both TCP and other SCP streams. Second, it improves smoothness in streaming and ensures low, predictable latency. This distinguishes it from TCP's jittery steady-state congestion avoidance policy that is based on linear growth and one-half rate reduction. In this paper, we present a description and analysis of SCP, and an evaluation using actual Internet-based experiments. 1

We develop Feedback Control real-time Scheduling (FCS) as a unified framework to provide Quality of Service (QoS) guarantees in unpredictable environments (such as ebusiness servers on the Internet). FCS includes four major components. First, novel scheduling architectures provide performance control to a new category of QoS critical systems that cannot be addressed by traditional open loop scheduling paradigms. Second, we derive dynamic models for computing systems for the purpose of performance control. These models provide a theoretical foundation for adaptive performance control. Third, we apply established control methodology to design scheduling algorithms with proven performance guarantees, which is in contrast with existing heuristics-based solutions relying on laborious design/tuning/testing iterations. Fourth, a set of controlbased performance specifications characterizes the efficiency, accuracy, and robustness of QoS guarantees. The

this paper, we present our experience with application-aware adaptation in the context of Odyssey, a platform for mobile data

A key feature of tomorrow’s operating systems and runtime environments is their ability to adapt. Current state of the art uses an ad-hoc approach to building adaptive software, resulting in systems that can be complex, unpredictable and brittle. We advocate a modular and methodical approach for building adaptive system software based on feedback control. The use of feedback allows a system to automatically adapt to dynamically varying environments and loads, and allows the system designer to utilize the substantial body of knowledge in other engineering disciplines for building adaptive systems. We have developed a toolkit called SWiFT that embodies this approach and helps system designers construct, analyze and visualize the behavior of their system. SWiFT provides a framework for composing simple feedback mechanisms that operate within limited domains, and for dynamically reconfiguring them in response to drastic changes in the environment. The result is a system that is efficient and predictable across a wide range of operating conditions. We describe three SWiFT applications to demonstrate the feasibility of this technology. 1

In this paper we propose to use feedback control to automatically allocate disk bandwidth in order to match the rate of disk I/O to the real-rate [13] needs of applications. We describe a model for adaptive resource management based on measuring the relative progress of stages in a producer-consumer pipeline. We show how to use prefetching to transform a passive disk into an active data producer whose progress can be controlled via feedback. Our progress-based framework allows the integrated control of multiple resources. The resulting system automatically adapts to varying application rates as well as to varying device latencies. 1 Introduction Real-rate applications [13] have specific disk I/O rate and throughput requirements that are driven by real-world demands. Examples of applications with real-rate disk I/O requirements include multimedia applications, real-time databases, and Internet servers. Real-rate applications suffer from uneven I/O throughput on conventional systems. To...