Turducken: Hierarchical Power Management for Mobile Devices

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Turducken Hierarchical Power Management for
Mobile Devices

• Jacob Sorber, Nilanjan Banerjee,
• Mark Corner, Sami Rollins

University of Massachusetts, Amherst
http//prisms.cs.umass.edu/hpm
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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 isnt this a reality?
• Mobility leads to variable connectivity
• Limited energy necessitates shutting laptop off
• The result is we dont even try!

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Tension in Maintaining Availability

• The laptop can remain activeavailable for
  communication
• System lifetime is severely limited
• The laptop can be suspendedextending 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
• Dont know when to wake up
• Systems lean toward longer lifetime
• Goal A system that is always available with
  extended lifetime

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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

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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

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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

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Use the Right Device for the Job
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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

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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

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HPM Hardware Design
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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

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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

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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

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Hardware Implementation
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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

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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
• LaptopMote
• LaptopPDAMote
• Experiments take a long time
• Extrapolate from a set of measured data points

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Effect of Consistency

• Measure the impact of maintaining consistency
• System wakes periodicallyvary 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

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Results Web Prefetching

• PDA is the right device for the job
• For always-on operation, Turducken lasts up to 10
  times longer

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Results E-Mail

• More interactive use reduces opportunities for
  Turducken to save power
• Turducken still lasts up to 6 times longer

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Power-By-Tier Web Caching
Laptop
LaptopMote
Full Turducken

• LaptopMote 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

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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

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Results Web Prefetching

• With no network mote prevents laptop from waking
• Turducken performs well over a variety of
  connectivity patterns

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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

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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

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Turducken Hierarchical Power Management for
Mobile Devices

• Jacob Sorber, Nilanjan Banerjee,
• Mark Corner, Sami Rollins

University of Massachusetts, Amherst
http//prisms.cs.umass.edu/hpm
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Turducken Whats In The Name?