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Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingMasters ThesisPresented byWissam ChedidAdvisorDr. Chansu YuDecember 2nd, 2003Outline• Power trends• Power Management, Dynamic Voltage Scaling (DVS) • MPEG• DVS for MPEG decoding• Experimental framework• Results• Conclusion

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Outline• Power trends• Power Management, Dynamic Voltage Scaling (DVS) • MPEG• DVS for MPEG decoding• Experimental framework• Results• Conclusion

Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingPower Trends• Power= CV2f, Power density= CV2f/Area• New processors:- More integration Higher C- Faster clocks Higher f- Smaller die Smaller Area• More power consumption• More and more power density

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Power TrendsWatts/cm2

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10

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Pentium®Pentium® Pro

Pentium® II

Pentium® III* “New Microarchitecture Challenges in the Coming Generations of* “New Microarchitecture Challenges in the Coming Generations of CMOS Process Technologies” CMOS Process Technologies” –– Fred Pollack, Fred Pollack, Intel Corp. Micro32 conference key note Intel Corp. Micro32 conference key note -- 1999. Courtesy 1999. Courtesy AviAvi MendelsonMendelson, Intel., Intel.Pentium® 4

’93 ’95 ’97 ’99 ’01 ’03 ’05 ’07

Nuclear Reactor

Hot PlateDynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingOutline• Power trends• Power Management, Dynamic Voltage Scaling (DVS) • MPEG• DVS for MPEG decoding• Experimental framework• Results• Conclusion

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Power Management Techniques• Static Power Management– Offline, during design time.– Estimate power consumption and find power-efficient improvements on different hardware and software levels.• Dynamic Power Management– Online, during runtime.– Monitor running system behavior and apply power-reduction techniques accordingly.Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingDynamic Voltage Scaling (DVS)• Power= CV2f• Reducing supply voltage V will reduce power quadratically• Problem:– It incurs more propagation delay and thus, forces a reduction in clock frequency f,Dynamic Voltage Scaling Techniques for Power-efficient MPEG Decoding

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Dynamic Voltage Scaling (DVS)Dynamic Voltage Scaling Techniques for Power-efficient MPEG Decoding1.2 V300 MHz

1.225 V400 MHz

1.35 V533 MHz

1.5 V600 MHz

1.6 V667 MHz

VoltageFrequency

.975 V300 MHz

1.05 V450 MHz

1.05 V533 MHz

1.15 V677 MHz

1.15 V733 MHz

VoltageFrequency

Transmeta Crusoe processor

Mobile Intel PentiumIII processor

Dynamic Voltage Scaling (DVS)• Power= CV2f• Reducing supply voltage V will reduce power quadratically• Problem:– It incurs more propagation delay and thus, forces a reduction in clock frequency f,– which means longer execution time, i.eperformance degradation ?Dynamic Voltage Scaling Techniques for Power-efficient MPEG Decoding

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Example: Always-On• Power is still consumed during idle timeVoltage / frequency

(V) (Mhz)

Time(ms)

1.8 / 120

1.6 / 100

1.4 / 80

1.2 / 60

1.0 / 401 3 5 8 9 11 12

Task 1 Idle Task 2 Idle Task 3 Idle

Average Power ~ 388.8 (Always On)

Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingExample: On/Off mechanism• Turn off the CPU during idle timeVoltage / frequency

(V) (Mhz)

Time(ms)

1.8 / 120

1.6 / 100

1.4 / 80

1.2 / 60

1.0 / 401 3 5 8 9 11 12

Task 1 Task 2 Task 3

Average Power ~ 388.8 (Always On)Average Power ~ 247.4 (On/Off)Dynamic Voltage Scaling Techniques for Power-efficient MPEG Decoding

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Average Power ~ 388.8 (Always On)Average Power ~ 247.4 (On/Off)

Example: DVS• DVS adjusts V and f to replace power-wasting idle time with useful execution cyclesVoltage / frequency

(V) (Mhz)

Time(ms)

1.8 / 120

1.6 / 100

1.4 / 80

1.2 / 60

1.0 / 401 5 9 12

Task 1 Idle Task 2 Idle Task 3 Idle

Task 1

Task 2

Task 3

Average Power ~ 147.8 (DVS)

Number of clock cycles 2*120 = 4*60Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingDynamic Voltage Scaling (DVS)

Dynamic Voltage Scaling Techniques for Power-efficient MPEG Decoding• Two questions for applying DVS : – Q: which applications are targeted by DVS ?A: DVS is best used for applications whose workload varies over time, like MPEG decoding.– Q: Who is going to predict the workload and adjust the voltage and frequency accordingly ?A: Workload can be predicted on different levels: CPU, OS, and application.• Our scheme is an application-based DVS for MPEG decoding

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Outline• Power trends• Power Management, Dynamic Voltage Scaling (DVS) • MPEG• DVS for MPEG decoding• Experimental framework• Results• Conclusion� Overview� MPEG encoding� MPEG decoding

• MPEG video compression is used in many current and emerging products (HDTV, DVD players, video conferencing, PDAs, etc.)• MPEG video requires:– Less storage space– Less transmission bandwidth• MPEG (Moving Picture Expert Group) is an ISO/IEC (International Organization for Standardization/International Electro-technical Commission) standard.

Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingMPEG

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• MPEG compression relies on:– Eye’s inability to resolve high frequency color changes– Spatial redundancy (or redundancy within each frame)– Temporal redundancy (or redundancy between adjacent frames)Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingMPEG: Encoding

* * ““MPEGMPEG--2: The Basics of how it Works2: The Basics of how it Works””, , Hewlett Packard LabHewlett Packard LabDynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingMPEG: Encoding

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MPEG: Decoding• MPEG decoding facts:– Different frame types (I,P,B) require different decoding time per byte.– Linear relationship between the ‘number of clock cycles’ and the ‘frame size’.0

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BIPDynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingOutline• Power trends• Power Management, Dynamic Voltage Scaling (DVS) • MPEG• DVS for MPEG decoding• Experimental framework• Results• Conclusion � Key issues� Workload estimation� Voltage averaging

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Voltage / frequency(V) (Mhz)

Time(ms)

1.8 / 120

1.6 / 100

1.4 / 80

1.2 / 60

1.0 / 40

Frame 1 Idle Frame 2 Idle Frame 3 Idle

DVS for MPEGFrame 1

Frame 2

Frame 3

Workload (number of clock cycles)

Dynamic Voltage Scaling Techniques for Power-efficient MPEG Decoding• Key issues: – Accurate prediction of future workload– Voltage/frequency setting– Decode frame on time for display

Voltage/frequency

Max. decoding time(e.g. 33ms) Display 2 Display 3Display 1DVS for MPEG

Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingVoltage / frequency

(V) (Mhz)

Time(ms)

1.8 / 120

1.6 / 100

1.4 / 80

1.2 / 60

1.0 / 40

Frame 1 Idle Frame 2 Idle Frame 3 Idle

Frame 1

Frame 2

Frame 3

Workload (number of clock cycles)

Voltage/frequency

Max. decoding time(e.g. 33ms) Display 2 Display 3Display 1

• Solution: – Frame size and type Number of clock cycles– MPEG frame rate Max. decoding time– V ~ f = number of cycles / Max. decoding time

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Voltage / frequency(V) (Mhz)

Time(ms)

1.8 / 120

1.6 / 100

1.4 / 80

1.2 / 60

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DVS for MPEGFrame 1

Frame 2

Display 1 Display 2 Display 3

• DVS Problems: voltage/frequency are estimated to decode a frame just on time for display.Frame 3Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingFrame 3

Voltage / frequency(V) (Mhz)

Time(ms)

1.8 / 120

1.6 / 100

1.4 / 80

1.2 / 60

1.0 / 40

DVS for MPEGFrame 1

Frame 2

Frame 1

Display 1 Display 2 Display 3

• DVS Problems:– Frame over-estimated more power consumed– Frame under-estimated miss display DroppedFrame 3

Frame 2Dynamic Voltage Scaling Techniques for Power-efficient MPEG Decoding

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Workload Estimation• Proposed DVS estimation techniquesDynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingWorkload Estimation: regressionDynamic Voltage Scaling Techniques for Power-efficient MPEG Decodingnumber of cycles = 50 * frame size + 4020185

• Regression (previous work)

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Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingFor each frame i :

1- Get frame_sizei

2- estimate_number_of_cyclei = actual_linear_equation(frame_sizei)

3- Get real_number_of_cyclei after decoding the frame

4- Recalculate actual_linear_equationbased on all previous frame_size0…iand real_number_of_cycle0…i using the linear regression model

Workload Estimation: regression• Regression algorithm:

Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingWorkload Estimation: regression• Regression algorithm main problem: very computationally expensive

y = b0 + b1*x

b1= (∑x*y – n*x*y ) / (∑x2 – n*x2)

b0= y – b1*x

where y = number of cycles

x = frame size

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Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingWorkload Estimation: interval-avg• Interval-avg (proposed technique) with simple average calculation in each interval

Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingFor each frame i :

1- Get frame_sizei

2- Find interval[k] where frameibelongs according to its frame_sizei

3- estimate_decode_timei = Avg_value_in_interval[k]

5- Get real_number_of_cyclei after decoding the frame

6- Recalculate Avg_value_in_interval[k] = Average(real_number_of_cycle0…i)

Workload Estimation: interval-avg• Interval-avg (proposed technique) with simple average calculation

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Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingWorkload Estimation: interval-avg• Interval-avg problem: many frames will be under-estimated and dropped

Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingWorkload Estimation: interval-max• Interval-max (proposed technique) with simple and safe estimation

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Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingFor each frame i :

1- Get frame_sizei

2- Find interval[k] where frameibelongs according to its frame_sizei

3- estimate_decode_timei = Max_value_in_interval[k]

5- Get real_number_of_cyclei after decoding the frame

6- If real_number_of_cyclei > Max_value_in_interval[k] then Max_value_in_interval[k] = real_number_of_cyclei

Workload Estimation: interval-max• Interval-max (proposed technique) with simple and safe estimation

Voltage / frequency(V) (Mhz)

Time(ms)

1.8 / 120

1.6 / 100

1.4 / 80

1.2 / 60

1.0 / 40

Voltage Averaging TechniqueFrame 1

Frame 2

Frame 3

Average Power ~ 135.6 (DVS only)

Display 2 Display 3Display 1Dynamic Voltage Scaling Techniques for Power-efficient MPEG Decoding• Voltage averaging is implemented on top of the previous estimation techniques for more power saving

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Average Power ~ 135.6 (DVS only)

Voltage / frequency(V) (Mhz)

Time(ms)

1.8 / 120

1.6 / 100

1.4 / 80

1.2 / 60

1.0 / 40Frame 1

Frame 2

Frame 1 Frame 2

Average Power ~ 130.5 (DVS with voltage averaging)

Frame 3

Display 2 Display 3Display 1Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingVoltage Averaging Technique• Voltage averaging is implemented on top of the previous estimation techniques for more power saving

Outline• Power trends• Power Management, Dynamic Voltage Scaling (DVS) • MPEG• DVS for MPEG decoding• Experimental framework• Results• Conclusion � Simulation framework� Simulation workload

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Estimated voltage

Estimated frequency

Experimental FrameworkFrame type and size

Proposed DVS estimation techniques

Estimated number of cycles

Frame rateVoltage/

frequency scaling

and averaging

(Max. decoding time)

MPEG workload (Movie)

SimpleScalarsimulator

BerkeleyMPEGplayer Exact number of cycles

(frame-by-frame Statistics)

Power estimator

(~V2f)

QoSestimator

Power statistics

QoSstatisticsDynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingProposed techniques Modified tools Developed tools

MPEG workload (Movie)

Estimated voltage

Estimated frequency

Frame type and size

Proposed DVS estimation techniques

Estimated number of cycles

Frame rateVoltage/

frequency scaling

and averaging

(Max. decoding time)

SimpleScalarsimulator

MPEG player Real number of cycles

(frame-by-frame Statistics)

Power estimator

(~V2f)

QoSestimator

Power statistics

QoSstatistics

Simulation Workload: Movie clipsMPEG

workload (Movie)

48610701088B frames

12242881P frames

12210741I frames

352x240592x252320x240Resolution

30 fps23.976 fps25 fpsFrame Rate

Movie (High motion)Animation (High motion)Animation (low motion)Type

UnderSiegeThe AnimatrixRed’s NightmareTitle

Dynamic Voltage Scaling Techniques for Power-efficient MPEG Decoding

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Outline• Power trends• Power Management, Dynamic Voltage Scaling (DVS) • MPEG• DVS for MPEG decoding• Experimental framework• Results• Conclusion� Power� QoSSimulation Results: Power

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RegressionDynamic Voltage Scaling Techniques for Power-efficient MPEG Decoding (*)

(*) Ideal DVS is the regular DVS with ideal perfect estimation

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• Voltage averaging effect on Power68

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Simulation Results: Power

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Dynamic Voltage Scaling Techniques for Power-efficient MPEG DecodingSimulation Results: Power

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Simulation Results0.9

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• Voltage averaging effect on QoSDynamic Voltage Scaling Techniques for Power-efficient MPEG Decoding

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Simulation Results• Interval effect on QoS0

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Simulation Results• Power/QoS tradeoff for different interval-size0

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Outline• Power trends• Power Management, Dynamic Voltage Scaling (DVS) • MPEG• DVS for MPEG decoding• Experimental framework• Results• ConclusionConclusion

Dynamic Voltage Scaling Techniques for Power-efficient MPEG Decoding• DVS estimation techniques for power-efficient MPEG decoding: regression, interval-max, and interval-avg• Voltage averaging technique• Results:– Up to 83% power saving over On/Off mechanism– As low as 0.4% frames dropped

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ConclusionDynamic Voltage Scaling Techniques for Power-efficient MPEG Decoding• Interval-max algorithm, although the simplest to implement, looks to be the most promising:– Best QoS (~0.4% frames dropped)– Good power saving (~80% over On/Off)– Perfectly predictable when changing ‘interval size’ to balance Power/QoS factors– Best candidate for future work researching this Power/QoS tradeoffs

Thank You