Power Optimizations ForWindows PlatformsPat StemenSenior Program ManagerWindows Platform Architecture GroupMicrosoft Corporation

Key Takeaways

Enable system designers to optimize Windows Vista power policy for energy efficiencyProvide guidance on platform design best practices for energy efficiency

Agenda

Energy EfficiencyEvaluating Energy EfficiencyConfiguring Windows Vista Power PolicyOther Windows Vista Power OptimizationsPlatform Design Best Practices

Energy Efficiency Introduction

Energy efficiency enables more than extended mobile PC battery life

Regulatory compliance for desktop and server systemsIncreased density of server deploymentsOperational energy expense reduction

Improving Energy Efficiency

Evaluate system power consumptionConfigure platform hardware and software policies

Trade performance for power savingsExamples

Enable a short monitor blanking timeoutEnable power save mode for 802.11 Wi-Fi adapter

Use energy-efficient hardware componentsInstall energy-efficient preload software

Evaluating Energy Efficiency

Methods to measure mobile PC battery lifeFirst, choose a scenario

Idle, DVD playback, Industry-standard benchmark

Perform run-down tests for first-level validationMeasure full-charge to empty drain duration

Repeat several times and average

Instrumented systems can be used to validate fine-grained changes

E.g., changes in video device / driver power management

Desktop and server power consumptionAverage AC power consumption

Evaluating Energy Efficiency

Indirect indicators of system power consumption

Effective use of deep processor idle statesObserve with Perfmon, PwrTest, or processor vendor utilities

Effective use of processor performance statesSystem should be in lowest performance state when processor utilization is low for maximum power savings

Observe with Perfmon or PwrTest

Default platform timer tick intervalPlatform timer should be at the default 15.6 ms value

Use event logging to see when applications change the timer frequency

Mobile PC Power Consumption

*Example Thin-and-Light Platform, Windows Vista RTM Idle

Display 43%Blanking, Dimming

Graphics

8%Processor 9%Perf, Idle States

Network 4%802.11 Power Save

HDD 5%Spin-down, DIPMChipset 21%

11.5 WAverage Power Consumption

IHV-Specific Technologies

Windows Power Policy

Windows Vista power policy defaults are generalized for multiple platforms and scenarios

“Balanced” power plan by defaultAdaptive behaviors enabled where possibleTimeouts are conservative

System manufacturers may configure policy for aggressive power savings

Help improve mobile PC battery lifeMeet regulatory compliance guidelines

System Idle Timeouts

Save power by turning off components after a period of inactivity

E.g., Turn off the display after 5 minutes without user input

Notable timeoutsDisplay / monitor blanking

Hard disk drive (HDD)

System Sleep, Hibernate

Display Idle Timeout

Turns off the display after a period of user inactivity

Display is ~40% of mobile PC power budget

External displays require 20W -> 100W+

Reduce the display timeout to increase power savingsFriendly Name Turn off the display

Description Specify how long your computer is inactive before the display turns off

GUID 3c0bc021-c8a8-4e07-a973-6b14cbcb2b7e

PowerCfg Alias VIDEOIDLE

Balanced Defaults 20 minutes (AC) 5 minutes (DC)

Sleep Idle TimeoutPlaces the computer to sleep after a period of inactivity

Most systems consume 1-3 W in Sleep

Less for mobile PCs

Application requests for system availability are considered

E.g., System stays on for PVR, music streamingFriendly Name Put the computer to sleep

Description Specify how long your computer is inactive before going to sleep

GUID 29f6c1db-86da-48c5-9fdb-f2b67b1f44da

PowerCfg Alias STANDBYIDLE

Balanced Defaults 60 minutes (AC) 15 minutes (DC)

Hard Disk Idle Timeout

Spins down HDD media after a period of disk read / write inactivity

Power savings varies by disk model

Typically 100-400mW on mobile HDDsFriendly Name Turn off hard disk after

Description Specify how long your hard drive is inactive before the disk turns off

GUID 6738e2c4-e8a5-4a42-b16a-e040e769756e

PowerCfg Alias DISKIDLE

Balanced Defaults 60 minutes (AC) 30 minutes (DC)

Processor Power Management

Detailed configuration in power policy:Min and max range of processor frequency

Parameters that influenceTarget performance state calculation

Idle state promotion/demotion

Care must be taken when tuning processor policies

Tuning must be platform-specific

Attend the processor power management tuning chalk talk

Reference public processor power management paper for more details

Domain Idle AccountingDetermines how the power manager calculates idle for performance states

Only applicable to systems with more than 1 logical processor

When enabled…

Idle time accrued only when all processors in the domain are idle

Favors performance

Windows Vista default

When disabled…

Idle time accrued when any processor in the domain is idle

Favors power savings

Processor will tend to stay in lowest performance state more often with domain idle accounting disabled

Attend SYS-C315 Tuning Processor Power Management

802.11 Power Save ModeChanges the polling rate of the 802.11 wireless adapter

Saves power by periodically turning the radio on / off

Requires a spec-compliant AP implementation

Power savings may be up to 600-700mW with Maximum Power SavingsFriendly Name Power Saving Mode

Description Control the power saving mode of wireless adapters

GUID 12bbebe6-58d6-4636-95bb-3217ef867c1a

PowerCfg Alias n/a

Balanced Defaults

Maximum Performance (AC)

Maximum Performance (DC)

Active State Power Management

Allows PCI Express links to enter low power idle states

Enabled in policy by default in Windows Vista

Requires native OS control of PCI Express features

See References for ASPM paper on WHDCFriendly Name Link State Power Management

Description Specifies the ASPM link policy to use when capable links are idle

GUID ee12f906-d277-404b-b6da-e5fa1a576df5

PowerCfg Alias n/a

Balanced Defaults

Moderate Power Savings (AC)

Maximum Power Savings (DC)

USB Selective Suspend

Selective suspend has large impact on system power consumption

Frequent DMA prevents effective utilization of processor idle states

Inability to use processor idle states may reduce mobile PC battery life by ~30%

USB devices must support selective suspend

Particularly when integrated into mobile platforms

Validate your platform or device is properly using selective suspend

Ensure effective use of processor idle states

USB Selective Suspend

Allows USB devices to suspend when they are idle

Enables the USB scheduler to turn offReduces DMA activity and increases processor idle state utilization

Power policy is global for all USB controllers and devicesFriendly Name USB Selective Suspend Setting

Description Specify whether USB selective suspend is turned on or off

GUID 48e6b7a6-50f5-4782-a5d4-53bb8f07e226

PowerCfg Alias n/a

Balanced Defaults

Disabled (AC) Enabled (DC)

Windows Search And Indexing

Indexing activity integrated into power policy

Controls the level of system indexing activity

Power modes match system power plan defaults

High PerformanceAll items are indexed, system-wide crawls are allowed

BalancedOnly high and normal-priority items are indexed, system-wide crawls are disabled

Power SaverOnly high-priority items are indexed, such as arriving e-mail

Windows Search And Indexing

Friendly Name Power Saving Mode

Description Specify power savings mode for Search and Indexing

GUID c1dd9fd6-ff5b-4270-8ab6-d48f1c40506a

PowerCfg Alias n/a

Balanced Defaults

High Performance (AC) Balanced (DC)

SATA AHCI Link Power Management

Allows SATA links to opportunistically enter low-power modes

Device-Initiated and Host-Initiated (DIPM, HIPM) power management

DIPM disabled by default in Windows VistaAllows lower-power AHCI link states

Limited disk compatibility issues

Requires Microsoft native SATA driver (msahci.sys)Registry Key HKLM\SYSTEM\CurrentControlSet\Services\

msahci\Controller0

Value (Binary) DIPMEnabled , 0x01

Default Disabled

Sleep Power Policies

Friendly Name Required Idleness to Sleep

Description Specify the amount of processor idleness required for the system to automatically sleep

GUID 81cd32e0-7833-44f3-8737-7081f38d1f70

PowerCfg Alias

n/a

Balanced Defaults

80% (AC) 80% (DC)

Sleep Idle Detection Threshold

Configures the amount of processor idle required for the system to sleep

Set to 0% to allow power manager to ignore CPU utilization when determining idle

System will aggressively enter sleep

Wake On Timer

Enables the system to wake on timerE.g., scheduled task, Media Center PVR

Disable wake on timer to prevent spurious wake events

Most appropriate for mobile PCsSome PCs already do this on DC power with EC/BIOS implementation

Will disable any timer-based wakeMedia center PVR

Windows Update

Doze to Hibernate

… and any other timer

Wake On Timer

Friendly Name Allow Windows to wake on Timer

Description Allow Windows to automatically wake your computer on a timer for scheduled tasks and other programs

GUID bd3b718a-0680-4d9d-8ab2-e1d2b4ac806d

PowerCfg Alias n/a

Balanced Defaults

Enabled (AC) Enabled (DC)

USB Host Controller Power State

USB host controllers armed for wake by default in Windows Vista

When entering sleep, host controllers will be placed in D2 if system supports wake from USB

Will keep power planes on if USB wake enabled

New USB registry option allows the host controller to enter D3

If no wake-armed devices are connected when system sleeps

Helps improve S3 battery life

USB Host Controller Power State

RequirementsSystem supports wake from USBACPI-enumerated USB controllers_PRW indicates lowest wake state >= S3_S3D == 0x2 (S3 -> D2)

Registry Key HKLM\SYSTEM\CurrentControlSet\Servicces\USB

Value (DWORD) ForceHcD3NoWakeArm == 0x1

Default Disabled

Power Optimization Benefits

Power policy changes have tangible impact on energy efficiency

PolicyDefault Value

Modified Value

Domain Idle Accounting Enabled Disabled

HDD Idle Timeout 30 minutes 2 minutes

SATA AHCI DIPM Disabled Enabled

802.11 Power Save Mode

Maximum Performance

Maximum Power Savings

Search and Indexing Balanced Power Saver

ScenarioDefault Runtime Average

Modified Runtime Average

Idle 235 minutes 253 minutes (+7%)

Power Optimization Benefits

DetailsIntel Core 2 Duo-based systems with integrated (GMA 950) graphics1 GB RAM, 60GB SATA HDDWindows Vista RTM, build 6000Latest drivers from manufacturer web site

Platform Design Best Practices

Review preload software for energy efficiency

Compare battery life of clean install to preload Work with ISVs and IHVs on energy efficiency improvements

Also scrutinize IHV software services and value add applicationsIntegrate with Vista power policy

Platform Design Best Practices

USB opportunitiesValidate USB-connected value-add devices support selective suspend

Fingerprint readers, webcams, etc

Avoid integrated USB hubsProcessor idle state utilization impactS3 resume delaysNeed to power the hub device itself

Platform Design Best Practices

Design and integrate low-power devices

Engage with IHVs to integrate device power management with Microsoft Vista power policyAttend the “Designing Power Friendly Devices” session

SYS-T309Speaker: Barnes Cooper, Intel CorporationIn this room, 2:00pm, after lunch

Call To Action

Evaluate energy efficiency and battery life on your platformTailor Windows Vista power policy to hardware platformDesign hardware and preload software for energy efficiency and power savings

Additional ResourcesWeb Resources

Power Policy Configuration and Deployment in Windows Vista http://www.microsoft.com/whdc/system/pnppwr/powermgmt/PMpolicy_Vista.mspx

Windows Vista Energy Conservation http://www.microsoft.com/whdc/system/pnppwr/powermgmt/VistaEnergyConserv.mspx

Related SessionsSYS-T300 – “Designing Power Friendly Devices”

SYS-T494 – “PCs and Energy Efficiency: Implications for IHVs”

SYS-C316- “How To Power Optimize Your Windows Platform

SYS-C315-”Tuning Processor Power Management”

E-mail:

Onnow @ microsoft.com

Battlife @ microsoft.com

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