Reducing the Energy Usage of Office Applications

Jason Flinn

M. Satyanarayanan

Carnegie Mellon University

Eyal de Lara

Dan S. Wallach

Willy Zwaenepoel

Rice University

2

Motivation

Energy is a vital resource in mobile computing

Previous work shows value of energy-aware adaptation Reduce fidelity Requires modification to application source code

Can this work without source code?Middleware-based proxy can help!

3

Validation

Common office applications can be made energy-aware Puppeteer uses well-defined data format and API Modified PowerPoint to reduce energy usage

Preview of results: Energy reductions up to 49% for some activities Proxy approach modifies PowerPoint behavior Other opportunities for increased energy-efficiency

4

Outline

Motivation

Background: Puppeteer

Energy benefits of adaptation

Other opportunities for extending battery lifetime

Future work and conclusions

5

Component-Based Adaptation

Documents often stored on a central file serverMust download and edit on a mobile clientCan save time and energy by editing a low-fidelity version

Server Client

skeleton

high-fidelity componentreintegrated

on save

reintegrated on save

missing component

6

Server

Puppeteer

DataServer

Client

PowerPointDocuments Client

ProxyServerProxy

TranscodedDocuments

Server proxy parses and transcodes documentsClient proxy uses external API to interact with PowerPoint

How much energy can component-based adaptation save?

Uses well-defined data formats, exported APIs

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Measuring Application Energy Usage

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0 50 100 150 200 250

Time (seconds)

Po

wer

(W

atts

)

Digital multimeter samples laptop power useApplications mark start and end of eventsEnergy usage is integral of power over time

EventStart

EventEnd

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Benchmark Presentations

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A B C D E F G H I J

Siz

e (M

B)

Full-Quality

Distilled

Benchmark consists of 10 PowerPoint presentationsSize and effect of distillation vary

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Experiment: Loading Documents

Client: IBM 560X laptop with 2 Mb/s wireless networkServer: Wall-powered desktop

Client runs NT, PowerPoint, Puppeteer client proxyServer runs NT, Apache, Puppeteer server proxy

Measure energy used to load documents: From Apache (native mode) Using Puppeteer (distilling out multimedia data)

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Energy Benefit for Loading Documents

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500

1000

1500

2000

2500

3000

3500

4000

A B C D E F G H I J

En

erg

y (J

ou

les)

Native

Puppeteer (Distilled)

Average energy usage reduced 40%!

Oops!

With simple filter, energy usage reduced 49%!

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Experiment: Editing Documents

Load documents on the client

Measure energy needed to page through document for: Full-quality version Distilled version

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Energy Benefit for Editing Documents

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600

700

800

A B C E F G H I J

En

erg

y (J

ou

les)

Full Quality

Distilled

Distillation reduces paging energy 13%Benefit less on subsequent traversals of document

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Reducing Computational Fidelity

Activity No pause 100 ms. pauseSpelling + Auto-Correct 1.9% 2.2%Grammar-Checking 3.1% 1.1%Office Assistant 9.5% 4.8%

Overhead

How much energy is used by background activities?

Not a lot to be gained by disabling most activities . . .

But, the Office Assistant is quite expensive!

14

Experiment: Autosave Frequency

Documents are saved on the client Autosaves over network prohibitively expensive! Reducing frequency saves energy But, greater possibility of losing data!

Measure additonal power savings for autosave frequency: One minute (very expensive) Five minutes (less expensive) No autosave (optimal savings)

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Effect of Autosave Frequency

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8

9

A B C D E F G H I J

Po

wer

(W

atts

)

1 Minute Autosave

5 Minute Autosave

No Autosave

Average energy reduction of 11%

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Outline

Motivation

Puppeteer: component-based adaptation

Energy benefits of adaptation

Other opportunities for extending battery lifetime

Future work and conclusions

17

Comparing Puppeteer and Native Mode

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0.5

1

1.5

2

2.5

3

A B C D E F G H I J

No

rmal

ized

En

erg

y

Native (Baseline)

Puppeteer

Mystery: Why does Puppeteer take less time and energy to load a presentation than native mode?

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Effect of Network Power Management

Hypothesis: power management slows down transfer Network receiver disabled for 100 ms. periods Wireless bandwidth 2 Mb/s In effect, a high bandwidth*delay product (25 KB) Socket buffer and receive window only 8 KB Native mode uses only 1 connection Puppeteer uses up to 4 connections

Verified this hypothesis by measuring: With 64KB buffer sizes Without network power management

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Network Power Management Results

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1.5

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2.5

3

A B C D E F G H I J

No

rmal

ized

En

erg

y

Native (Baseline)

Puppeteer

Native (64KB Buffers)

Native (No PM)

With 64 KB buffers, native mode uses 26% less energyDisabling power management saves additional 18%

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Disk Power Management

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700 750 800 850 900

Time (seconds)

Po

wer

(W

atts

)

Autosave

Disk spinning = Wasted Energy

Disk power management predicts periods of inactivityAfter autosave, waits for additional activityDisk in high-power state for 30 seconds

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Transparent Power Management

Applications and power mgmt. layer don’t communicate Power management balances performance & energy Tries to minimize impact on applications Difficult without knowledge of application activity

Transparent power management can help! Applications provide hints about their activities OS combines hints from all applications OS chooses the optimal power mgmt. settings

Applications

TransparentPower

ManagementLayer

CPU

Disk

Network

Power Mgmt.Settings

Hints

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PowerPoint and Power Management

Puppeteer could provide PM hints for PowerPoint

1. Signals start and end of large transfers Power management disabled during transfers Uses 18% less energy, 22% less time

2. Signals when regular autosave is occurring Can spin-down disk immediately after autosave Uses 4% less energy

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Outline

Motivation

Puppeteer: component-based adaptation

Energy benefits of adaptation

Other opportunities for extending battery lifetime

Future work and conclusions

24

Future Work

System support for energy-aware applications Currently open-source implementation (Linux) Monitors supply and demand, adjusts fidelity Port to closed-source environment (Windows)

Transparent power management Create API for expressing application hints Develop algorithms that combine hints Investigate other hardware devices (CPU)

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Conclusions

No one magic bullet for reducing PowerPoint energy useBut, many opportunities for significant energy reduction

Reducing data fidelity Reducing computational fidelity Transparent power management

Puppeteer provides a mechanism for achieving reductions Proxy approach requires no source-code modification Takes advantage of exported APIs

Other potential domains for this work: Other Microsoft Office applications Web browsers