SungKyunKwan Univ.

1VADA Lab.

Dynamic Voltage Scaling

SungKyunKwan Univ.

2VADA Lab.

Energy Efficient Software for General Purpose Computing, Trevor Pering, UC-Berkeley

SungKyunKwan Univ.

3VADA Lab.

Introduction: Research Spectrum

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4VADA Lab.

Introduction: My Contributions

• Simulator: Instruction-level Energy Estimation

• Software: Energy Efficient Algorithms• OS: Voltage Scheduling Algorithms ***• OS: Multiprocessing for Energy• Microprocessor: Dynamic Caches

SungKyunKwan Univ.

5VADA Lab.

Processor Systems:high Power

• Thinkpad (Pentium) 0.3 Hours/AA• InfoPad (ARM) 0.8 Hours/AA• Toshiba Portable (486) 0.9 Hours/AA• Newton (ARM) 2.0 Hours/AA• Device (Processor) Processor System Lif

etime

SungKyunKwan Univ.

6VADA Lab.

Do We Just Optimize Power?

• Operations per Battery Life:• Minimize Energy Consumed per

Operation• Operations per Second:• Maximize Throughput

Operations/ second

SungKyunKwan Univ.

7VADA Lab.

Ultra-low power Infopad Project

SungKyunKwan Univ.

8VADA Lab.

Voltage Scaling

• Merely changing a processor clock frequency is not an effective technique for reducing energy consumption. Reducing the clock frequency will reduce the power consumed by a processor, however, it does not reduce the energy required to perform a given task.

• Lowering the voltage along with the clock actually alters the energy-per-operation of the microprocessor, reducing the energy required to perform a fixed amount of work.

SungKyunKwan Univ.

9VADA Lab.

SungKyunKwan Univ.

10VADA Lab.

OS: Voltage Scaling

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11VADA Lab.

DVS

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12VADA Lab.

Dynamic Voltage Scaling

SungKyunKwan Univ.

13VADA Lab.

DVS Scheduling Frameworkµ

Pro

c. S

peed

Time

Start Deadline Start Deadline

Idle time represents

wasted energy

Lower speed,Lower voltage, Lower energy

Energy ~ Work • Speed

WorkWork

• Use real-time framework toconstrain task voltage scheduling

SungKyunKwan Univ.

14VADA Lab.

DVS SimulationS

peed

Time

S1 S2 S3 D1 D3 D2 Task Variance

Weather

Interrupts

User Input

Cache Behavior

Scheduling Overhead

IntercomIntercom

RealityTheory ImplementationSimulate run-time scheduler to

fully understand voltage-scaling behavior

SungKyunKwan Univ.

15VADA Lab.

Simulation InfrastructureGUI

Run-timeScheduler

VoltageScheduler

Applicationsupport libraries

MPEG Priority 80GUI Priority 23

MPEG Priority 80GUI Priority 23

Speed Priority

{ Frame_Start(deadline); Decode_MPEG_Frame(); Frame_Finish();}

{ Frame_Start(deadline); Decode_MPEG_Frame(); Frame_Finish();}Windowing

Cryptography

I/O Support

lpARM

MPEG

Develop support environment tomodel complete software system

SungKyunKwan Univ.

16VADA Lab.

Results: Run-Time Voltage Scaling

73%

58%

25%16%

65%

46%

15%20%

0%

20%

40%

60%

80%

100%

Audio GUI MPEG Audio &MPEG

To

tal

Sy

ste

m E

ne

rgy

DVS SimulationPost-Trace Optimal

Normalized to 3.3V

fixed-voltage processor

Combination of independent

benchmarks

• Dynamic Voltage Scalingsignificantly reduces energy dissipation!

SungKyunKwan Univ.

17VADA Lab.

Run-Time Performance AnalysisFrame Computation Histogram

0%

20%

40%

60%

80%

100%

Fixed-V Frame Execution Time

AudioGUIMPEG

DVS System Energy

0%

20%

40%

60%

80%

100%

To

tal S

ys

tem

En

erg

y

Basic AlgorithmAdjusted AlgorithmPost-Trace Optimal

Audio MPEG GUI

Software can automatically recognize and adjust for

bi-modal GUI distribution

0 2x deadline

Normalized to deadline at max processor speed

• Application characteristics strongly affectvoltage scaling performance

SungKyunKwan Univ.

18VADA Lab.

Variable Supply Voltage Block Diagram

• Computational work varies with time. An approach to reduce the energy consumption of such systems beyond shut down involves the dynamic adjustment of supply voltage based on computational workload.

• The basic idea is to lower power supply when the a fixed supply for some fraction of time.

• The supply voltage and clock rate are increased during high workload period.

SungKyunKwan Univ.

19VADA Lab.

Data Driven Signal Processing

The basic idea of averaging two samples are buffered and their work loads are averaged.

The averaged workload is then used as the effective workload to drive the power supply.

Using a pingpong buffering scheme, data samples In +2, In +3

are being buffered while In, In +1

are being processed.

SungKyunKwan Univ.

20VADA Lab.

Simplest Approach: Compute ASAP

SungKyunKwan Univ.

21VADA Lab.

Another Approach: Reduce Clock Frequency

SungKyunKwan Univ.

22VADA Lab.

Voltage Scheduling II

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23VADA Lab.

Evaluation: Algorithms

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24VADA Lab.

OS: Voltage Scheduling

SungKyunKwan Univ.

25VADA Lab.

Run-Time Scheduling Dynamicsµ

Pro

c. S

peed

Time

Thread accomplishing more than expected,

reduce speedDeadline exceeded,

increase speedHigher-priority

task

Run faster to make up lost time

Initial speed estimate

Optimal scheduleE(work)

Workload calculated to be average of previous frames

• Periodically re-evaluate schedule toadjust for unforeseen events

SungKyunKwan Univ.

26VADA Lab.

Vertical Layering

SungKyunKwan Univ.

27VADA Lab.

Optimal Scheduling• For a region spanned by a given task

specification, each point in time will either be scheduled at the minimum speed spanned by that task or else the task will not be scheduled to run at that point.

Algorithm• n tasks to schedule• O(n) speed settings to consider for each task• O(n) linked tasks requiring adjustment for

each setting: Total complexity: O(n 3 ) time.

SungKyunKwan Univ.

28VADA Lab.

SungKyunKwan Univ.

29VADA Lab.

SungKyunKwan Univ.

30VADA Lab.

SungKyunKwan Univ.

31VADA Lab.

SungKyunKwan Univ.

32VADA Lab.

SungKyunKwan Univ.

33VADA Lab.

SungKyunKwan Univ.

34VADA Lab.

SungKyunKwan Univ.

35VADA Lab.

References• [Lin97] Lin et al., "Scheduling Techniques for Variable Voltage Low

Power Designs," ACM Transactions on Design Automation of Electronic Systems, vol. 2, no. 2, pp. 81-97, 1997.

• [Govil95] - Extended simulation with practical algorithms on traces of UNIX workstations

• [Kuroda98] - Implementation of DVS processor to mitigate effects of process variation

• [Ishihara98] - Dynamic voltage scaling with non- constant capacitances

SungKyunKwan Univ.

36VADA Lab.

• S. Kunii, "Means of Realizing Long Battery Life in Portable PCs," Proceedings of the IEEE Symposium on Low Power Electronics, Oct. 1995, pp. 12-3.

• M. Culbert, "Low Power Hardware for a High Performance PDA," Proceedings of the Thirty-Ninth IEEE Computer Society International Conference, Mar. 1994, pp. 144-7.

• T. Ikeda, "ThinkPad Low-Power Evolution," Proceedings of the IEEE Symposium on Low Power Electronics, Oct. 1995, pp. 6-7.

• A. Chandrakasan, A. Burstein, and R.W. Brodersen, "A Low Power Chipset for Portable Multimedia Applications," IEEE Journal of Solid State Circuits, Vol. 29, Dec. 1994, pp. 1415-28.

• M. Horowitz, T. Indermaur, and R. Gonzalez, "Low-Power Digital Design," Proceedings of the IEEE Symposium on Low Power Electronics, Oct. 1994, pp. 8-11.

• D. Lidsky and J. Rabaey, "Early Power Exploration - A World Wide Web Application," Proceedings of the Thirty-Third Design Automation Conference, June 1996.

• T. Burd, Low-Power CMOS Cell Library Design Methodology, M.S. Thesis, University of California, Berkeley, UCB/ERL M94/89, 1994.

SungKyunKwan Univ.

37VADA Lab.

• A. Chandrakasan, S. Sheng, and R.W. Brodersen, "Low-Power CMOS Digital Design," IEEE Journal of Solid State Circuits, Apr. 1992, pp. 473-84.

• Advanced RISC Machines, Ltd., ARM710 Data Sheet, Technical Document, Dec. 1994.

• Integrated Device Technology, Inc., Enhanced Orion 64-Bit RISC Microprocessor, Data Sheet, Sep. 1995.

• Intel Corp., Embedded Ultra-Low Power Intel486TM GX Processor, SmartDieTM Product Specification, Dec. 1995.

• A. Stratakos, S. Sanders, and R.W. Brodersen, "A Low-voltage CMOS DC-DC Converter for Portable Battery-operated Systems," Proceedings of the Twenty-Fifth IEEE Power Electronics Specialist Conference, June 1994, pp. 619-26.

• J. Bunda, et. al., "16-Bit vs. 32-Bit Instructions for Pipelined Architectures," Proceedings of the 20th International Symposium on Computer Architecture, May 1993, pp. 237-46.

• Advanced RISC Machines, Ltd., Introduction to Thumb, Developer Technical Document, Mar. 1995.

SungKyunKwan Univ.

38VADA Lab.

• J. Bunda, W.C. Athas, and D. Fussell, "Evaluating Power Implications of CMOS Microprocessor Design Decisions," Proceedings of the International Workshop on Low Power Design, Apr. 1994, pp. 147-52.

• P. Freet, "The SH Microprocessor: 16-Bit Fixed Length Instruction Set Provides Better Power and Die Size," Proceedings of the Thirty-Ninth IEEE Computer Society International Conference, Mar. 1994, pp. 486-8.

• T. Burd, B. Peters, A Power Analysis of a Microprocessor: A Study of an Implementation of the MIPS R3000 Architecture, ERL Technical Report, University of California, Berkeley, 1994.

• J. Montanaro, et. al., "A 160MHz 32b 0.5W CMOS RISC Microprocessor," Proceedings of the Thirty-Ninth IEEE International Solid-State Circuits Conference - Slide Supplement, Feb. 1996, pp. 170-1.

• J. Bunda, Instruction-Processing Optimization Techniques for VLSI Microprocessors, Ph.D. Thesis, The University of Texas at Austin, 1993.

• R. Gonzalez and M. Horowitz, "Energy Dissipation in General Purpose Processors," Proceedings of the IEEE Symposium on Low Power Electronics, Oct. 1995, pp. 12-3.

SungKyunKwan Univ.

39VADA Lab.

S. Gary, et. al., "The PowerPC 603 Microprocessor: A Low-Power Design for Portable Applications," Proceedings of the Thirty-Ninth IEEE Computer Society International Conference, Mar. 1994, pp. 307-15.

A. Chandrakasan, Low Power Digital CMOS Design, Boston: Kluwer Academic Publishers, 1995.

C. Nagendra, et.al., "A Comparison of the Power-Delay Characteristics of CMOS Adders,” Proceedings of the International Workshop on Low Power Design, Apr. 1994, pp. 231-6.

T. Callaway and E. Swartzlander, "Optimizing Arithmetic Elements for Signal Processing," VLSI Signal Processing, Vol. 5, New York: IEEE Special Publications, 1992, pp. 91-100.

T. Biggs, et. al., "A 1 Watt 68040-Compatible Microprocessor," Proceedings of the IEEE Symposium on Low Power Electronics, Oct. 1994, pp. 8-11.

J. Lorch, A Complete Picture of the Energy Consumption of a Portable Computer, M.S. Thesis, University of California, Berkeley, 1995.

A. Chandrakasan, M. Srivastava, and R.W. Brodersen, "Energy Efficient Programmable Computation," Proc of the Seventh International Conference on VLSI Design, Jan. 1994, pp. 261-64.

Intel Corp. and Microsoft Corp., Advanced Power Management (APM): BIOS Interface Specification, Technical Document, Feb. 1996.

M. Wieser, et. al., "Scheduling for Reduced CPU Energy," Proceedings of the First USENIX Symposium on Operating Systems Design and Implementation, Nov. 1994, pp. 13-23.

K. Govil, E. Chan, and H. Wasserman, "Comparing Algorithms for Dynamic Speed-Setting of a Low-Power CPU," Proceedings 1st ACM International Conference on Mobile Computing and Networking, Nov. 1995, pp. 13-25.

V. Tiwari, et. al., "Instruction Level Power Analysis and Optimization of Software," Journal of VLSI Signal Processing.