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Power Management

Power Management. Power: A New Resource. Energy is consumed by Display WiFi card CPU Disk Memory Access : :. WiFi Card. Operating Mode Send/Recv Mode (900-1400 mW) Sleep Mode (50mW) Proxy Assisted Power-Friendly Streaming to Mobile Devices P. Shenoy and P. Radkov, MMCN 2002.

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Power Management

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  1. Power Management

  2. Power: A New Resource • Energy is consumed by • Display • WiFi card • CPU • Disk • Memory Access : :

  3. WiFi Card • Operating Mode • Send/Recv Mode (900-1400 mW) • Sleep Mode (50mW) Proxy Assisted Power-Friendly Streaming to Mobile Devices P. Shenoy and P. Radkov, MMCN 2002

  4. LCD Display • Backlight modes • Superbright (2.8W) • Power Save (1.72W) Reducing Backlight Power Consumption for Streaming Video Applications on Mobile Handheld Devices S. Pasricha et. al. Workshop on Embedded Systems for Real-Time Multimedia, October 2003

  5. CPU • Running at • 300MHz (22W) • 700MHz (30W) • 1GHz (40W) Practical Voltage Scaling for Mobile Multimedia Devices W. Yuan, K. Nahrstedt, ACM MM 2004

  6. Power and Media Streaming • Power Consumed When • Receive packets • Decode • Display

  7. Idea • Send video stream that is power-friendly

  8. Proxy-Assisted Power-Friendly Streaming to Mobile Devices P. Shenoy and P. Radkov MMCN 2002

  9. Architecture Here’s my energy budget for decoding + network reception and max resolution server/proxy client

  10. Architecture OK, what should I send? server/proxy client

  11. Information Needed • Map stream properties to energy requirement • Need to know decoding time of a frame

  12. Frame Decoding Time

  13. Decoding Time • As a function of size • As a function of resolution

  14. Estimating Frame Decoding Time

  15. Transcoding • If current stream would exceed client decoding energy budget • Need to transcode by reducing quality

  16. Transcode to what? E = estimated energy needed while E > energy budget reduce quality by ε E = estimate energy needed

  17. Transcoded Streams server/proxy client

  18. Estimating Frame Decoding Time

  19. Reducing NIC Energy • NIC has two modes : active/sleep • Client can activate NIC only when packets are expected.

  20. Normal Transmission

  21. Burst Transmission I will start transmitting at 10:12:54.86 pm

  22. Transcoded Streams OK, I will wake up at t + kd I will start transmitting at time t server/proxy client

  23. Evaluation Frame Number

  24. Evaluation • NIC Idle Uptime: 2 – 20% • Energy Savings: 65 – 98%

  25. Power and Media Streaming • Power Consumed When • Receive packets • Decode • Display

  26. Reducing Backlight Power Consumption for Streaming Video Applications on Mobile Handheld Devices S. Pasricha et. al. ESTIMedia 2003

  27. Idea • If video is bright, can reduce backlight

  28. Intensity of an Image

  29. Perceived Intensity

  30. Reduction in Backlight

  31. Increment in Pixel Intensity

  32. Compensate Every Frame?

  33. How to compensate playback at this backlight level server/proxy client

  34. Evaluation • Savings: 350 – 650mW

  35. Energy Efficient Soft Real-Time CPU Scheduling for Mobile Multimedia Systems W. Yuan, K. Nahrstedt SOSP 2003

  36. Motivation • Mobile devices run on battery • How to save battery?

  37. Dynamic Voltage Scaling • Example: AMD Athlon 4 PowerOn {300, 500, 600, 700, 800, 1000}MHz • Energy  V2

  38. CPU Scheduler • When to execute a task • Howlong to execute it • Howfastto execute it

  39. Requirements • “I need C units of time, out of every T units.” • How to know C?

  40. Probability Distribution Cum. Prob. cycles

  41. Soft Real-Time Scheduling • EDF with budget C • If overrun budget, use available free time

  42. CPU Requirements • “I need C units of time, out of every T units.”

  43. Speed Schedule speed time

  44. Finding Speed Schedule • Let task execute at speed vx during cycle x • execution time: • energy per cycle: • expected energy:

  45. Optimize This • Minimize: • Subjected to:

  46. Implementation • Linux Kernel • AMD Athlon 4 • 716 lines of code

  47. Evaluation: Cycles

  48. Evaluation: Power Savings

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