Transcript L18_energy_managementx - Interactive Computing Lab

Energy Management
Uichin Lee
KAIST KSE
Mobile Processing Power –
Changing the Mobile Device
From http://www.ieee-infocom.org/2010/docs/Infocom2010_keynote.pdf
Chipset Business Evolving to System
Business
Integration is key to driving advanced functionality to mass market
From http://www.ieee-infocom.org/2010/docs/Infocom2010_keynote.pdf
Creating New Mobile, Computing and
CE Device Categories
From http://www.ieee-infocom.org/2010/docs/Infocom2010_keynote.pdf
But Major Gaps Exist
Battery Technology is Falling Behind
How do we balance battery life with performance and cost?
Energy Management
on Handheld Devices
Marc A. Viredaz, Lawrence S. Brakmo, William R. Hamburgen
HP Labs ACM Queue Oct. 2003
Itsy Platform
• Itsy goals (YR 2000):
– Small, powerful, flexible h/w platform
– Flexible, extensible, advanced s/w environment
• Base system
– StrongArm SA-1100 microprocessor
– 32MB DRAM & Flash Drive
– LCD display and touch screen
• Passive matrix gray scale
–
–
–
–
–
Li-ion battery (charges from USB)
2-axis accelerometer
Microphone
Jacks (headset, docking)
Daughtercard connecter
• Software
– Linux 2.0.30 w/ modified memory/flash-based file systems
– Power management capability
Ohm’s law, Power, Energy
• Ohm’s law: V=IR (=current*resistance)
I=V/R?
9v
2.2Ω
Voltage
drop = 16v
2kΩ
I=V/R?
• Power: watt (W) = 1 joule/second (J/s)
– Power (W) = VI= I2R
• Energy: (Ws, or Joule)
– Energy (Ws) = power (w) * time (s)
Power Measurement
• Voltages are directly measured.
• Currents are calculated from the
corresponding sense-resistor voltage drop.
• Elementary power domains are delimited
by dashed lines.
Power Consumption
Energy Saving Techniques
• Simple approach: if a unit is not used, turn off
or put into sleep mode
• But requires well structured h/w and s/w
design
• Inter-connected building blocks must independently
function and be independently powered on/off
• Operating systems (or applications) utilize measured
power values to balance performance and battery life
• Major power draws: processor, memory,
display, audio system, wireless networking
Processor
StrongARM SA-1100
Processor
• Frequency or/and voltage scaling: Power ∝ f·v2
– f: operating frequency, v: voltage
Voltage Scaling in Strong Arm SA-1100
59Mhz at 0.79v
 251Mhz at 1.65v
J.Pouwelse, K.Langendoen, and H. Sips, “Dynamic Voltage Scaling on a Low-Power Microprocessor”, MOBICOM2001
Processor: How to Scale?
• How to scale voltage/frequency?
power
Low frequency
?
High frequency
...
time
Watts
Watts
Eactive
Eactive
Eidle
t
t
Critical Power Slope: Understanding the Runtime Effects of Frequency Scaling, ICS2002
Processor: Critical Power Slope
m  mcritical
mcritical  P
f min
Power
f
: energy efficient to run at lower freq
 Pidle
min
mcritical
Pf min
m  mcritical
: energy efficient to run at higher freq
Pidle
f
min Frequency
fmin: min operating frequency
Pfmin: power consumption at freq fmin
Pidle: idle power consumption
Critical Power Slope: Understanding the Runtime Effects of Frequency Scaling, ICS2002
Memory
• DRAM typically has four states:
– Activate/pre-charge: read/write happen (most energy consuming)
– Fast lower-power: short-term sleeping (w/ fast wake-up time: ~10ns, and
consumes only half of the active power)
– Self-refresh: only refreshing is happening (much less power consumption,
requires several 100 cycles)
– Deep power-down: refreshing stopped (lost data)
Figure from: http://research.microsoft.com/pubs/102932/flicker-tr-2009.pdf
Display
• LCD itself consumes minimal energy, yet display
front- and back-light dominates..
– Possible to dim lights of “light” pixels (for energy saving)
• Organic light-emitting diode (OLED)
– Better quality than LCD (fast response), but it’s emissive
and can’t make use of ambient light (energy consuming..)
Display: Chameleon (MobiSys 2011)
Chameleon: A Color-Adaptive Web Browser for Mobile OLED Displays, Mian Dong and Lin Zhong, MobiSys 2011
Display: Chameleon (MobiSys 2011)
• Changing Web Content for OLED friendly?
– Generate Device Specific OLED Power Model
– Color Transformation of GUI Objects and
Images
– Keep Color Consistency for Each Website
– Calculate Color Maps Offline
– Give User Options
Wireless Networking
• Technologies
– WiFi, Bluetooth
– 2G/3G/4G cellular communications
• Power consumption: BT < WiFi < 2/3/4G
• Caveats:
– bit/joule must be considered
– bit/joule varies with data rate
Cool-Tether: Energy Efficient On-the-fly WiFi Hot-spots using Mobile Phones, CoNext 2009
Energy Profile of Samsung Galaxy S2
• Accelerometer, compass << gyroscope, GPS
<< WLAN, WAN(3G/4G)