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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: 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
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
CPU • Running at • 300MHz (22W) • 700MHz (30W) • 1GHz (40W) Practical Voltage Scaling for Mobile Multimedia Devices W. Yuan, K. Nahrstedt, ACM MM 2004
Power and Media Streaming • Power Consumed When • Receive packets • Decode • Display
Idea • Send video stream that is power-friendly
Proxy-Assisted Power-Friendly Streaming to Mobile Devices P. Shenoy and P. Radkov MMCN 2002
Architecture Here’s my energy budget for decoding + network reception and max resolution server/proxy client
Architecture OK, what should I send? server/proxy client
Information Needed • Map stream properties to energy requirement • Need to know decoding time of a frame
Decoding Time • As a function of size • As a function of resolution
Transcoding • If current stream would exceed client decoding energy budget • Need to transcode by reducing quality
Transcode to what? E = estimated energy needed while E > energy budget reduce quality by ε E = estimate energy needed
Transcoded Streams server/proxy client
Reducing NIC Energy • NIC has two modes : active/sleep • Client can activate NIC only when packets are expected.
Burst Transmission I will start transmitting at 10:12:54.86 pm
Transcoded Streams OK, I will wake up at t + kd I will start transmitting at time t server/proxy client
Evaluation Frame Number
Evaluation • NIC Idle Uptime: 2 – 20% • Energy Savings: 65 – 98%
Power and Media Streaming • Power Consumed When • Receive packets • Decode • Display
Reducing Backlight Power Consumption for Streaming Video Applications on Mobile Handheld Devices S. Pasricha et. al. ESTIMedia 2003
Idea • If video is bright, can reduce backlight
How to compensate playback at this backlight level server/proxy client
Evaluation • Savings: 350 – 650mW
Energy Efficient Soft Real-Time CPU Scheduling for Mobile Multimedia Systems W. Yuan, K. Nahrstedt SOSP 2003
Motivation • Mobile devices run on battery • How to save battery?
Dynamic Voltage Scaling • Example: AMD Athlon 4 PowerOn {300, 500, 600, 700, 800, 1000}MHz • Energy V2
CPU Scheduler • When to execute a task • Howlong to execute it • Howfastto execute it
Requirements • “I need C units of time, out of every T units.” • How to know C?
Probability Distribution Cum. Prob. cycles
Soft Real-Time Scheduling • EDF with budget C • If overrun budget, use available free time
CPU Requirements • “I need C units of time, out of every T units.”
Speed Schedule speed time
Finding Speed Schedule • Let task execute at speed vx during cycle x • execution time: • energy per cycle: • expected energy:
Optimize This • Minimize: • Subjected to:
Implementation • Linux Kernel • AMD Athlon 4 • 716 lines of code