1 Lev Finkelstein ISCA/Thermal Workshop 6/2004

Overview

1. Motivation (Kevin)2. Thermal issues (Kevin)3. Power modeling (David)4. Thermal management (David)5. Optimal DTM (Lev)6. Clustering (Antonio)7. Power distribution (David)8. What current chips do (Lev)9. HotSpot (Kevin)

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Lev Finkelstein ISCA/Thermal Workshop 6/2004

What current chips do

Power and thermal management

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Controllers

• Inputs (power, temperature, etc.)• Response time• Tuning• Simplicity of implementation• Performance, reliability• Power management / thermal

management

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Controllers (cont’d)

• A non-trivial tradeoff

Performance Reliability

Cost

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Real processors:

• IBM* PowerPC* G3/G4 Cache throttling • AMD* PowerNow!* Technology• Transmeta* Longrun* technology• Intel® SpeedStep® technology• Enhanced Intel® SpeedStep technology

* Other names and brands may beclaimed as the property of others

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PowerPC G3 Microprocessor

• On-chip temperature sensor (junction temperature)– Based on differential voltage change across

2 diodes of different sizes – Implemented in PowerPC G3/G4 processors

• OS required for control• Instruction Cache Throttling used to

dynamically lower junction temperature

From Micro-35 tutorial

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Transmeta LongRun**

• LongRun power management– Code Morphing* software (processor-

internal)– Performance demands are determined by

sampling the idle time

• Crusoe* processor***

– Voltage changes in steps of 25 mV – Frequency changes in steps of 33 MHz

*Other names and brands may be claimed as the property of others

** Source: http://www.transmeta.com*** Data dated 2001

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Transmeta LongRun (cont’d)

• Idle time decrement V&f• Activity increment V&f (if possible)• Performance mode V&f adjustment

Source: http://www.transmeta.com/crusoe/longrun.html

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Previous Intel microprocessors1

• Thermal monitor mechanism• A two-point mechanism using voltage

scaling (for battery life)

1Information on Intel microprocessors is based on Efraim Rotem’s presentation in the TACS workshop 06/2004

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Thermal monitor

• Based on clock throttling• Full operational mode: maximal

frequency• Minimal operation mode: clocks are

stalled for a part of the duty cycle• Activation options:

– By OS (e.g., ACPI)– By a special hardware

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Static voltage scaling (for battery life)

• Performance mode – Maximal frequency & Vcc– AC outlet or set by user

• Power saving mode– Low frequency & Vcc– Upon request or while the user changed the

usage mode

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The Intel Pentium® M Processor

• Targets the mobile market• Improved power efficiency• Advanced ACPI interface• Enhanced SpeedStep architecture

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DVS in the Pentium M Processor

• Changes both voltage and frequency at the runtime

• Efficiently switches between different DVS control points

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Thermal sensors

Control

Thermal throttleXXooCC

Thermal ControlLogic

SoftwareControl

PROCHOT#XXooCC

Thermal throttleXooCC

Thermal throttleCritical ShutdownYooCC

CriticalpointExternal A/D

•Two thermal sensors•Maximal temperature reached throttling •Critical shutdown point reached shutdown

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Operation modes

• Software control mechanism (e.g., ACPI)– Track the junction temperature– Initiate the appropriate policy

• Self throttle– Digital temperature detector initiates one of

the power control cycles– Used as a fail-safe mechanism since it is

much faster than the software

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Enhanced Intel SpeedStep technology

• Implements DVS• Upon a thermal trigger or SW request,

CPU halts execution and locks PLL at a new frequency (a few sec)

• Once finished, the Vcc starts changing to the new value (order of 1mV/sec)

• Transition up is done in the reverse order

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DVS cycle

Clock

Vcc

Power

Switch Back

Switch

Clock

Vcc

Power

Switch Back

Switch Back

Switch Switch

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DVS transitions

• Frequency transition is fast enough to allow non-interrupted application execution

• DVS transitions can be utilized for energy and thermal control during the normal operation flow

• The target frequency and voltage are programmable by BIOS or OS

• Support for multiple voltage/ frequency points

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Adaptive policy (for battery life)

• Uninterrupted power state transition• User selectable policy• Increases frequency on demand, and

decreases power and frequency while idle for a long time

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Info

• More specific information on Pentium M will be available at Efraim Rotem’s presentation in the TACS workshop 06/2004

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ACPI and OSPM1

• ACPI = Advanced Configuration and Power Interface (an open industry specification)

• OSPM = Operating System-directed configuration and Power Management

• Cooling decisions are based on the application load and the thermal heuristics of the system

1Source: The ACPI specification 2.0, see http://www.acpi.info/

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Cooling policies

• Active cooling – a direct action by OSPM (e.g., turning on a fan)

• Passive cooling – reducing the power consumption (e.g., throttling)

• Critical trip points – shutdown

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Example of SW-based clock throttling

• P[%] = _TC1 * (Tn – Tn-1) + _TC2 * (Tn –Tt)

• Tn – current temperature

• Tt – target temperature

• Pn = Pn-1 + HW[-P]• Pn is in %

• The coefficients are set by the OEM