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Transcript
Power Motivation for design constraints of power consumption Power metrics Power consumption analysis in CMOS How can a logic designer control power? CS 150 - Spring 2007 – Lec #28 – Power - 1 “X-Internet” Beyond the PC Internet Computers Internet Users 500 Million Today’s Internet 1.5 Billion Automobiles 700 Million Telephones 4 Billion X-Internet Electronic Chips 60 Billion Forrester Research, May 2001 CS 150 - Spring 2007 – Lec #28 – Power - 2 Revised 2007 “X-Internet” Beyond the PC Millions 15000 10000 PC Internet 5000 CS 150 - Spring 2007 – Lec #28 – Power - 3 10 20 20 08 20 07 20 06 20 05 20 04 20 03 20 02 20 20 01 0 09 X Internet Year Forrester Research, May 2001 Cell Phones Phone w/voice command, voice dialing, intelligent text for short msgs MP3 player + headset, digital voice recorder “Mobile Internet” with a built-in WAP Browser Java-enabled, over the air programmable Bluetooth + GPRS Siemens SL45i Ericsson T68 Enhanced displays + embedded cameras CS 150 - Spring 2007 – Lec #28 – Power - 4 Shape of Things Phone + Messenger + PDA Combinations E.g., Blackberry 5810 Wireless Phone/Handheld Integration of PDA + Telephone PLUS Gateway to Internet and Enterprise applications 1900 MHz GSM/GPRS (Euroversion at 900 Mhz) SMS Messaging, Internet access QWERTY Keyboard, 20 line display JAVA applications capable 8 MB flash + 1 MB SRAM CS 150 - Spring 2007 – Lec #28 – Power - 5 Shape of Things to Come Danger “Hiptop” Full-featured mobile phone w/Internet Access Email + attachments/instant messaging + PIM Digital camera accessory End-to-end integration of voice + data apps Media-rich UI for graphics + sound Large screen + QWERTY keyboard Data nav: keyboard or push wheel Affordable (under $200) MIDI synthesizer for quality sound Multi-tasking of user actions Customizable ring tones and alerts to personalize hiptop experience CS 150 - Spring 2007 – Lec #28 – Power - 6 Important (Wireless) Technology Trends “Spectral Efficiency”: More bits/m3 Rapidly increasing transistor density Rapidly declining system cost CS 150 - Spring 2007 – Lec #28 – Power - 7 In the Physical World: Sensor Devices CS 150 - Spring 2007 – Lec #28 – Power - 8 Important (Wireless) Technology Trends Speed-Distance-Cost Tradeoffs Rapid Growth: Machine-toMachine Devices (mostly sensors) CS 150 - Spring 2007 – Lec #28 – Power - 9 Why Worry About Power? Portable devices: Handhelds, laptops, phones, MP3 players, cameras, … all need to run for extended periods on small batteries without recharging Devices that need regular recharging or large heavy batteries will lose out to those that don’t. Power consumption important even in “tethered” devices System cost tracks power consumption: Power supplies, distribution, heat removal Power conservation, environmental concerns In 10 years, have gone from minimal consideration of power consumption to (designing with power consumption as a primary design constraint! CS 150 - Spring 2007 – Lec #28 – Power - 10 Basics Power supply provides energy for charging and discharging wires and transistor gates. The energy supplied is stored & then dissipated as heat. Power: Rate of work being done wrt time Rate of energy being used P dw / dt Units: P E t Watts = Joules/seconds If a differential amount of charge dq is given a differential increase in energy dw, the potential of the charge is increased by: By definition of current: V dw / dq I dq / dt dw dq dw / dt P V I dq dt t w Pdt total energy A very practical formulation! If we would like to know total energy CS 150 - Spring 2007 – Lec #28 – Power - 11 Basics Warning! In everyday language, the term “power” is used incorrectly in place of “energy” Power is not energy Power is not something you can run out of Power can not be lost or used up It is not a thing, it is merely a rate It can not be put into a battery any more than velocity can be put in the gas tank of a car CS 150 - Spring 2007 – Lec #28 – Power - 12 This is how electric tea pots work ... Heats 1 gram of water 0.24 degree C 0.24 Calories per Second 1A 1V + - 1 Joule of Heat Energy per Second 1 Ohm Resistor 20 W rating: Maximum power the package is able to transfer to the air. Exceed rating and resistor burns. CS 150 - Spring 2007 – Lec #28 – Power - 13 Cooling an iPod nano ... Like a resistor, iPod relies on passive transfer of heat from case to the air Why? Users don’t want fans in their pocket ... To stay “cool to the touch” via passive cooling, power budget of 5 W If iPod nano used 5W all the time, its battery would last 15 minutes ... CS 150 - Spring 2007 – Lec #28 – Power - 14 Powering an iPod nano (2005 edition) Battery has 1.2 W-hour rating: Can supply 1.2 W of power for 1 hour 1.2 W / 5 W = 15 minutes More W-hours require bigger battery and thus bigger “form factor” -it wouldn’t be “nano” anymore! Real specs for iPod nano : 14 hours for music, 4 hours for slide shows 85 mW for music 300 mW for slides CS 150 - Spring 2007 – Lec #28 – Power - 15 0.55 ounces 12 hour battery life $79.00 1 GB CS 150 - Spring 2007 – Lec #28 – Power - 16 20 hour battery life for audio, 6.5 hours for movies (80GB version) Up from 14 24 hour battery life hours for 2005 iPod nano for audio Thinner than 2005 iPod nano 5 hour Up from 4 battery life hours for 2005 for photos iPod nano 12 hour battery life CS 150 - Spring 2007 – Lec #28 – Power - 17 Notebooks ... now most of the PC market Apple MacBook -- Weighs 5.2 lbs 8.9 in 1 in 12.8 in Performance: Must be “close enough” to desktop performance ... many people no longer own a desktop Size and Weight: Ideal: paper notebook Heat: No longer “laptops” -- top may get “warm”, bottom “hot”. Quiet fans OK CS 150 - Spring 2007 – Lec #28 – Power - 18 Battery: Set by size and weight limits ... Battery rating: 55 W-hour 46x energy than iPod nano. iPod lets you listen to music for 14 hours! At 2.3 GHz, Intel Core Duo CPU consumes 31 W running a heavy load under 2 hours battery life! And, just for CPU! Almost full 1 inch At 1 GHz, CPU consumes depth. Width and 13 Watts. “Energy saver” height set by available option uses this mode ... space, weight. CS 150 - Spring 2007 – Lec #28 – Power - 19 Battery Technology Battery technology has developed slowly Li-Ion and NiMh still the dominate technologies Batteries still contribute significantly to the weight of mobile devices Nokia 61xx 33% Handspring PDA - 10% Toshiba Portege 3110 laptop - 20% CS 150 - Spring 2007 – Lec #28 – Power - 20 55 W-hour battery stores the energy of 1/2 a stick of dynamite. If battery short-circuits, catastrophe is possibleCS... 150 - Spring 2007 – Lec #28 – Power - 21 CPU Only Part of Power Budget 2004-era notebook running a full workload. “other” GPU LCD Backlight CPU If our CPU took no power at all to run, that would only double battery life! LCD CS 150 - Spring 2007 – Lec #28 – Power - 22 Servers: Total Cost of Ownership (TCO) Machine rooms are expensive … removing heat dictates how many servers to put in a machine room. Reliability: running computers hot makes them fail more often CS 150 - Spring 2007 – Lec #28 – Power - 23 Electric bill adds up! Powering the servers + powering the air conditioners is a big part of TCO Thermal Image of Typical Cluster Rack Rack Switch QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. M. K. Patterson, A. Pratt, P. Kumar, “From UPS to Silicon: an end-to-end evaluation of datacenter efficiency”, Intel Corporation CS 150 - Spring 2007 – Lec #28 – Power - 24 How Do We Measure and Compare Power Consumption? One popular metric for microprocessors is: MIPS/watt MIPS, millions of instructions per second Typical modern value? Watt, standard unit of power consumption Typical value for modern processor? MIPS/watt reflects tradeoff between performance and power Increasing performance requires increasing power Problem with “MIPS/watt” MIPS/watt values are typically not independent of MIPS • Techniques exist to achieve very high MIPS/watt values, but at very low absolute MIPS (used in watches) Metric only relevant for comparing processors with a similar performance One solution, MIPS2/watt. Puts more weight on performance CS 150 - Spring 2007 – Lec #28 – Power - 25 Metrics How does MIPS/watt relate to energy? Average power consumption = energy / time MIPS/watt = instructions/sec / joules/sec = instructions/joule Equivalent metric (reciprocal) is energy per operation (E/op) E/op is more general - applies to more that processors also, usually more relevant, as batteries life is limited by total energy draw. This metric gives us a measure to use to compare two alternative implementations of a particular function. CS 150 - Spring 2007 – Lec #28 – Power - 26 Power in CMOS Vdd Switching Energy: Vdd pullup network energy used to switch a node i(t) v(t) 0 1 Calculate energy dissipated in pullup: pulldown C network v(t) t0 t1 GND t1 t1 t1 t0 t0 t0 Esw P(t )dt (Vdd v) i(t )dt (Vdd v) c (dv dt ) dt t1 t1 t0 t0 cVdd dv c v dv cVdd 1 2cVdd 1 2 cVdd Energy supplied 2 Energy stored 2 2 Energy dissipated An equal amount of energy is dissipated on pulldown CS 150 - Spring 2007 – Lec #28 – Power - 27 Switching Power Gate power consumption: Assume a gate output is switching its output at a rate of: activity factor f clock rate (probability of switching on any particular clock period) 1/f Pavg E t switching rate Esw Therefore: Pavg f 1 2 cVdd Chip/circuit power consumption: 2 Pavg Pavg n avg f 1 2 cavgVdd 2 number of nodes (or gates) CS 150 - Spring 2007 – Lec #28 – Power - 28 clock f Other Sources of Energy Consumption “Short Circuit” Current: Junction Diode Leakage : Vout I Vin Vin Vout Transistor drain regions “leak” charge to substrate. I I Vin 10-20% of total chip power Diode Characteristic V ~1nWatt/gate few mWatts/chip CS 150 - Spring 2007 – Lec #28 – Power - 29 Other Sources of Energy Consumption Consumption caused by “DC leakage current” (Ids leakage): Ids Vin=0 Vout=Vdd Ioff Transistor s/d conductance never turns off all the way Vgs Vth Low voltage processes much worse This source of power consumption is becoming increasing significant as process technology scales down For 90nm chips around 10-20% of total power consumption Estimates put it at up to 50% for 65nm CS 150 - Spring 2007 – Lec #28 – Power - 30 Controlling Energy Consumption: What Control Do You Have as a Designer? Largest contributing component to CMOS power consumption is switching power: Pavg n avg f 1 2 cavgVdd 2 Factors influencing power consumption: n: total number of nodes in circuit : activity factor (probability of each node switching) f: clock frequency (does this effect energy consumption?) Vdd: power supply voltage What control do you have over each factor? How does each effect the total Energy? Our design projects do not optimize for power consumption CS 150 - Spring 2007 – Lec #28 – Power - 31 Scaling Switching Energy per Gate Moore’s Law at work … Due to reduced V and C (length and width of Cs decrease, but plate distance gets smaller) Recent slope reduced because V is scaled less aggressively From: “Facing the Hot Chips Challenge Again”, Bill Holt, Intel, presented at Hot Chips 17, 2005. CS 150 - Spring 2007 – Lec #28 – Power - 32 Device Engineers Trade Speed and Power We can reduce CV2 (Pactive) by lowering Vdd We can increase speed by raising Vdd and lowering Vt We can reduce leakage (Pstandby) by raising Vt From: Silicon Device Scaling to the Sub-10-nm Regime Meikei Ieong,1* Bruce Doris,2 Jakub Kedzierski,1 Ken Rim,1 Min Yang1 CS 150 - Spring 2007 – Lec #28 – Power - 33 Customize processes for product types ... From: “Facing the Hot Chips Challenge Again”, Bill Holt, Intel, presented at Hot Chips 17, 2005. CS 150 - Spring 2007 – Lec #28 – Power - 34 Intel: Comparing 2 CPU Generations ... Find enough tricks, and you can afford to raise Vdd a little so that you can raise the clock speed! Clock speed unchanged ... Lower Vdd, lower C, but more leakage Design tricks: architecture & circuits CS 150 - Spring 2007 – Lec #28 – Power - 35