University of Massachusetts, Amherst

Turducken: Hierarchical Power

Management for Mobile Devices

Jacob Sorber, Nilanjan Banerjee,

Mark Corner, Sami Rollins†

http://prisms.cs.umass.edu/hpm

Batteries and Wireless: Two Achilles Heels

Imagine using a laptop like it was a desktop:

your mail is always fresh

your file system is always consistent

your web is always prefetched

instant messages are instantaneous

Why isn’t this a reality?

Mobility leads to variable connectivity

Limited energy necessitates shutting laptop off

The result is we don’t even try!

Tension in Maintaining Availability

The laptop can remain active—available for communication

System lifetime is severely limited

The laptop can be suspended—extending lifetime

System is not available

Compromise: wake periodically to communicate

More frequent = more available, shorter lifetime

Less frequent = less available, longer lifetime

The tension remains despite current methods

Don’t know when to wake up

Systems lean toward longer lifetime

Goal: A system that is always available with extended lifetime

Solution: Hierarchical Power Management

Hierarchical Power Management

Combine a range of embedded platforms into a single device

Perform tasks on the tier that best fits the task

Download email using PDA

Download large movies with laptop

Sleep high-power tiers when not needed

Focus on non-interactive use

Provide power-efficiency when NOT in use

Remove the human bottleneck

Allow new laptop functionality

Outline

HPM Design Principles:

Combine the Right Platforms

Use the right device for the job

Decompose Tasks

Design of an HPM Laptop

Implementation of Turducken

Hardware

Software

Experimental Results

Related Work and Conclusions

Combine the Right Platforms

More platforms = more overhead

Size, weight, and complexity

Suspend power

Transition cost between platforms

Still need to support a large range of power modes

Use few devices separated by orders-of-magnitude in power

Use the Right Device for the Job

40W

2W

0.04WSensor

PDA

Laptop

Simple computatio

nand storage

Download Web Pages

Very complex computation

Send/RecvMail

Tasks requiringlarge memory or

storage space

Pow

er

Need

s

Decompose Tasks

Not only separate platforms, but subdivide tasks

Tasks include common subtasks:

Checking for network connectivity

Service Discovery

Check for work to be done

Interact with user

Example:

Mote checks for a network, PDA checks for mail server

Laptop remains asleep until user reads the mail

Outline

HPM Design Principles:

Combine the Right Platforms

Use the right device for the job

Decompose Tasks

Design of an HPM Laptop

Implementation of Turducken

Hardware

Software

Experimental Results

Related Work and Conclusions

HPM Hardware Design

WakeControl

Higher Tier

LowerTier

WakeControl

Local Communication Link

Local Communication Link

Battery

Service Discovery

Task Execution

Tier Hardware (CPU, Memory, Storage)

HPM Software Design

Take advantage of transparent proxies

Proxies periodically perform service discovery and fetch content

Provide it on demand to higher tiers in system

Many applications are already distributed

Lower tiers act as proxy for higher tiers

Little or no application recoding and invisible to users

MailProxy

PDA

MailClient

LaptopMail

Server

Outline

HPM Design Principles:

Combine the Right Platforms

Use the right device for the job

Use the right number of devices

Design of an HPM Laptop

Implementation of Turducken

Hardware

Software

Experimental Results

Related Work and Conclusions

Hardware Implementation

Combines Laptop, PDA, and mote into a laptop

Laptop and PDA communicate via USB

PDA and mote via RS-232

Wakeup using relays

WiFi detector allows mote to detect 802.11 beacons

PDALaptop MoteUSB RS-232

Wake

Hardware Implementation

Applications

Time Synchronization

Can be completely performed by the mote

Lowest tier periodically synchronizes with remote time server

Web Prefetching

More complicated application which requires at least PDA

Mote detects wireless networks

PDA periodically fetches updates to frequently accessed pages

E-Mail

Involves user interaction

Both incoming and outgoing updates

Laptop accesses mail via proxy on the PDA

Evaluating Turducken

How does HPM affect battery lifetime?

Show results for a variety of workloads

Vary the consistency of the application

Vary the availability of the network

Consider three configurations

Laptop

Laptop+Mote

Laptop+PDA+Mote

Experiments take a long time

Extrapolate from a set of measured data points

Effect of Consistency

Measure the impact of maintaining consistency

System wakes periodically—vary frequency

Network is always present

Time Synchronization (please see paper)

Web Prefetching

Laptop routes network traffic through PDA

PDA periodically refreshes expired pages

E-Mail

System wakes with constant rate to send mail (2 min/hr)

PDA periodically checks for new mail and sends pending mail

Results: Web Prefetching

PDA is the right device for the job

For always-on operation, Turducken lasts up to 10 times longer

Wake Interval (minutes)

Lif

eti

me (

hou

rs)

Results: E-Mail

More interactive use reduces opportunities for Turducken to save power

Turducken still lasts up to 6 times longer

Wake Interval (minutes)

Lif

eti

me (

hou

rs)

0

100

200

300

400

500

600

700

Avera

ge P

ow

er

(mW

)

Mote Active

Mote Suspend

PDA Active

PDA Suspend

Laptop Active

Laptop Suspend

Laptop Laptop+Mote

Full Turducken

Power-By-Tier: Web Caching

Laptop+Mote shows cost of adding unnecessary platforms

Turducken replaces 400mW of laptop active power with 25mW on PDA

Laptop suspend power is the greatest limiting factor: try hibernation

Effect of Network Availability

Measure the impact of intermittent connectivity

Network is present with varying probability

Mote wakes at a fixed interval

Only wakes PDA when network is available

Only show results for Web Prefetching

Probability of WiFi

Lif

eti

me (

hou

rs)

Results: Web Prefetching

With no network mote prevents laptop from waking

Turducken performs well over a variety of connectivity patterns

Related Work

Wake-On-Wireless [Shih, et al]

Low-power radio receives wakeup messages

Requires in-network support

Focus on when to wake up

Wireless optimizations [Anand, et al], Disk Spindown [Helmbold, et al], Multiple radios [Pering, et al], Multiple processor cores [Mayo & Ranganathan]

none provide orders-of-magnitude scaling of power

Conclusions

Always-on availability and extended battery life

Hierarchical Power Management

Integrate multiple independent platforms

Pass control between tiers

Suspend unneeded tiers

Use proxy-based approach

Little or no application recoding

Always-on operation for up to 10x as long

University of Massachusetts, Amherst

Turducken: Hierarchical Power

Management for Mobile Devices

Jacob Sorber, Nilanjan Banerjee,

Mark Corner, Sami Rollins†

http://prisms.cs.umass.edu/hpm

Turducken: What’s In The Name?