Controlling Energy Demand In Mobile Computing Systems

by Ellis, Carla Schlatter

• ISBN13: 9781598291285
• ISBN10: 1598291289
• Format: Paperback
• Copyright: 2007-03-15
• Publisher: Morgan & Claypool

Summary

This lecture provides an introduction to the problem of managing the energy demand of mobile devices. Reducing energy consumption, primarily with the goal of extending the lifetime of battery-powered devices, has emerged as a fundamental challenge in mobile computing and wireless communication. The focus of this lecture is on a systems approach where software techniques exploit state-of-the-art architectural features rather than relying only upon advances in lower-power circuitry or the slow improvements in battery technology to solve the problem. Fortunately, there are many opportunities to innovate on managing energy demand at the higher levels of a mobile system. Increasingly, device components offer low power modes that enable software to directly affect the energy consumption of the system. The challenge is to design resource management policies to effectively use these capabilities.

Table of Contents

Introduction	p. 1
Lecture Overview	p. 3
System Energy Models and Metrics	p. 5
Models of How Power/Energy is Consumed in Mobile Devices	p. 5
Power and Energy Models	p. 5
Discrete Power States of Device Components	p. 8
Scaling Power Mechanisms	p. 13
Simplified Battery Model	p. 15
Energy Metrics	p. 16
Measurement and Tools	p. 18
Measurement Techniques	p. 18
Energy Estimation by Simulation	p. 20
Management of Device Power States	p. 23
Idleness Defined and Detected	p. 23
Policies for Power State Transitions	p. 24
Transitions Among High and Low Power States	p. 24
Transitions Among Multiple Power States	p. 27
Duty Cycling Modes	p. 29
Granularity of Transitions	p. 31
Modifying Request Patterns to Increase Idle Periods	p. 32
Caching and Prefetching	p. 32
Memory Management	p. 36
Summary	p. 38
Dynamic Voltage Scheduling (DVS)	p. 39
Workload and Quality of Service Criteria	p. 40
About Time and Idle Time	p. 40
System Models of Frequency/Voltage Scaling	p. 41
Interval-Based Approaches	p. 43
DVS for Real-Time Tasks	p. 46
Intratask DVS	p. 47
Intertask DVS	p. 50
Toward the General-Purpose Environment	p. 53
Summary	p. 54
Multiple Devices-Interactions and Tradeoffs	p. 55
Impact of Device Energy Management on Other Components	p. 55
Energy-Aware Alternatives	p. 57
Computation Versus Communication	p. 57
Storage Alternatives	p. 58
Networking Alternatives	p. 60
Platform Tiers	p. 62
Putting it all Together-Whole Systems	p. 63
Summary	p. 66
Energy-Aware Application Code	p. 69
Application Interfaces to Assist System-Level Power Management	p. 69
Usage Hints	p. 69
System Calls for More Flexibility in Timing	p. 72
OS-Application Information Flow to Enable Adaptation	p. 73
Frameworks for System Feedback	p. 73
Adaptation Through Fidelity	p. 75
Developing Applications for Energy Efficiency	p. 77
Summary	p. 77
Challenges and Opportunities	p. 79
On Improving Hardware Capabilities	p. 79
On System Software as a Focal Point	p. 80
On Engaging Application Designers and Users	p. 80
Going Forward	p. 81
References	p. 83
Author Biography	p. 89
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