Power Management In Windows Vista Pat Stemen Program Manager Windows Platform Architecture Group Microsoft Corporation

Power Management In Windows Vista

• Pat Stemen Program Manager Windows Platform Architecture Group Microsoft Corporation

Agenda

• Windows Vista Power Management Goals

• Windows Vista Power Management Feature Overview

• Power Policy Configuration Tasks

• S3 Resume Performance

• Resume Performance Measurements
• Measuring with PwrTest

Windows Vista Power Management Goals

• Simplify the user experience

• Improve the reliability of sleep transitions

• Ensure deterministic behavior
• Improve visibility into power management actions
• Provide extensive diagnostic tracing

• Enable maximum energy savings by default

• Help extend Mobile PC battery life
• Reduce desktop power consumption

• Enable easy deployment of power management configuration

• Enterprise PC energy savings

Windows Vista Power Policy

• Simplified for the user

• 3 power plans by default

• Group policy control of power settings

• Extensible power policy settings model and data store

• All power policy settings are GUID-based
• All users manipulate the same set of power policy objects
• Power setting access can be restricted
• Highly integrated device and application power management
• Development of custom power policy applications and tools is simplified

Power Policy Setting Scope

• All power policy is stored on a per-machine basis

• A single set of power schemes for the entire machine
• All users have access to power schemes
• Do not need to be an administrator
• One active power scheme at any point in time
• Last set active power scheme is used when no users are logged in, initial boot
• Only the user at the console session can apply a new power scheme to the system

Power Policy Security

• Windows Vista enables access control for individual power settings

• E.g., Ability to change “Prompt for password on resume” power setting can be restricted to administrators only
• By default, all authenticated users have access to change all power settings
• Power policy access rights can be restricted
• Apply a power scheme
• Create/delete a power scheme
• Restore power scheme defaults
• Access control manipulated via powercfg.exe
• Powercfg.exe – setsecuritydescriptor POWER_SETTING “[SDDL Security Descriptor String]”
• SDDL string reference on MSDN

Group Policy

• Windows Vista power policy can be enforced with group policy

• Enables IT professionals to easily reduce PC energy consumption and associated cost
• E.g., enforce monitor idle and system sleep timeouts
• Potential cost savings and benefits
• http://www.energystar.gov/powermanagement
• All power settings included with Windows Vista can be enforced
• Power Options in Control Panel indicates if group policy overrides are active

Reliable Sleep Transitions

• Windows Vista promotes the use of sleep as the default off state

• Requires reliable, fast and deterministic sleep transitions

• Failed transitions were the primary sleep adoption blocker in previous versions of Windows

• Lead to great user frustration and distrust of power management
• Investigations indicate component vetoes are the primary cause
• Application, service or driver willingly prevents the sleep transition

Reliable Sleep Transitions

• Sleep transitions will succeed

• Vista will not query user mode components when entering sleep
• Drivers may not veto sleep transitions
• User-mode notification (PBT_APMSUSPEND) will continue to be sent
• Timeout to process event has been reduced from 20 seconds to 2 seconds

• Applications, services, and drivers must be prepared for this change

• Proper design and test is imperative

Integrating with Windows Power Management

• Windows Vista enables all components to integrate with system-wide power policy

• Including device drivers and software applications
• Enables rich device power management
• Beyond run time idle detection
• Extends current policy preference to components
• Provides mechanisms for definition and installation of custom power settings
• Exposes a broad set of power event notifications

Integrating with Windows Power Management

• Benefits of integrating with Windows Power Policy

• Simplicity for users
• Allows the entire platform to respond to the user’s current power policy
• All power settings appear in Windows Power Options
• No need to provide additional configuration UI
• Including custom 3rd party power settings
• Allows for true OEM power management innovation and value
• Examples
• Mobile graphics power management
• Session CPA013 details an example by ATI
• Chipset power management
• Media playback applications

Brightness Controls

• Windows Vista integrates display brightness into power policy

• Enables simple control of brightness for users
• Each power scheme has an associated brightness level preference
• Distinct AC and DC values
• Brightness controls are also exposed in Mobility Center
• Requires ACPI brightness object support
• See session CPA002 “ACPI in Windows Vista” for implementation details

Away Mode

• Away Mode addresses media sharing scenarios

• PC is required to be running (S0), but look and sound off

• Away Mode is not a new power state

• System remains in S0
• Power consumption is the same as S0
• Processor performance, fan speed may dynamically adjust based on workload, power policy

• When entering Away Mode…

• Display is turned off, audio is muted
• Keyboard and mouse input are ignored

• Away Mode does not replace other availability solutions, such as Wake-on-LAN (WoL)

• Away Mode is not recommended for enterprise deployments

Away Mode Support

• Away Mode does not expose a user interface

• Away mode is enabled dynamically by applications or in the registry
• Key: HKLM\System\CCS\Control\Power
• Value: AwayModeEnabled (0x1: Enabled, 0x0: Disabled)
• SetThreadExecutionState(ES_AWAYMODE_REQUIRED | ES_CONTINUOUS)
• When enabled, any user-initiated sleep trigger will enter Away Mode
• Sleep button, media remote, Start Menu power button, etc.
• Any hardware button event will exit Away Mode
• Includes sleep button on media remote
• The system may idle into sleep (S3) based on current power policy

• Away Mode is available in all Windows Vista SKUs

• No hardware or BIOS dependencies

Hybrid Sleep

• Saves Hibernate file, then enters Standby

• Normally, resume is from memory image
• If power is lost, system resumes from hibernate image on disk

• Allows for a simple shutdown metaphor

• Users do not need to understand or choose between Standby and Hibernate; just “Off”
• Default off mode for Windows Vista desktops

• Provides increased reliability

• Data and system state are always backed by non-volatile storage

Hybrid Sleep

• Core implementation

• System device drivers are told the platform is entering the S4 state
• IRP_MN_SET_POWER Parameters.Power.State == PowerSystemHibernate
• Enables a hibernation context (system state on disk) to be generated
• Device drivers should save enough context to resume from the S4 state
• Platform firmware is placed in the S3 state

Hybrid Sleep

• Wake-capable devices should support wake from all sleep states

• S1, S3, S4
• Users do not want their system to sleep into S1 state
• Consumes unnecessary power when compared to S3
• May be noisy with case and processor fans running
• Note: Hybrid Sleep transitions will not lighten to S1 state if a driver fails IRP_MN_QUERY_POWER for S3 or S4

• You may need to special case Hybrid Sleep transitions in your driver for wake-capable devices

• Only necessary if your device supports wake from S3, but not S4
• Devices that are wake-capable from S3 should be wake-capable from Hybrid Sleep
• Hybrid Sleep transitions will appear to be S4 transitions unless your driver is modified

Common Power Policy Configuration Tasks

• Powercfg command-line tool can be used to configure power policy

• Included with Windows Vista
• Suitable for most factory floor configuration tasks
• Import/export new power schemes
• Updating power policy defaults
• Adjusting individual power settings
• E.g., changing processor performance state min, max

Common Power Policy Configuration Tasks

• Powercfg tool supports textual aliases for common power policy GUIDs

• Every Windows Vista power scheme and setting is identified by a GUID
• Use aliases in place of GUID parameters to powercfg
• “powercfg /aliases” displays the entire list
• Example: S3 idle timeout
• Power setting GUID
• “{29f6c1db-86da-48c5-9fdb-f2b67b1f44da}”
• Powercfg alias
• “STANDBYIDLE”

Common Power Policy Configuration Tasks

• Configure power settings within a specific power scheme

• Set AC, DC values for individual power settings
• Note: Every power setting is in a power setting subgroup
• Note: Use – setdcvalueindex to change power setting policy on battery power

Common Power Policy Configuration Tasks

• Rename a power scheme

• Update power scheme friendly name, description
• Strings can be localized
• Use “@dllpath,-resourceID” syntax
• E.g., “@%SystemRoot%\system32\powrprof.dll,-14”

Common Power Policy Configuration Tasks

• Export a power scheme

• Stores the contents of a power scheme on disk
• Power scheme can be imported on other systems
• Use to distribute custom power schemes across enterprise deployment

Common Power Policy Configuration Tasks

• Import a power scheme

• Restores a power scheme from a file containing an exported power scheme
• Allows IT, OEM to install custom power scheme on multiple systems
• Specify a well-known GUID when importing the new scheme to enable group policy enforcement

Common Power Policy Configuration Tasks

• Update default power schemes

• Copies the current power schemes to the default user registry hive
• Enables OEM, IT to have custom schemes, values restored when user restores defaults

Optimizing S3 Resume Performance

• Fast resume performance is critical to the PC user experience

• Users want instant PC availability, appliance-like behavior
• Sleep states are preferred to boot, shutdown
• Boot and shutdown have longer on, off latencies
• Sleep states (S3, S4) on desktops have almost the same power consumption as shutdown (S5)

• Sleep states are the default off mode in Windows Vista

• S3 for mobiles
• Hybrid Sleep for desktops

Optimizing S3 Resume Performance

• Windows Vista core technologies enable PCs to have almost instantaneous S3 resume performance

• Improvements to the kernel power manager IRP dispatch mechanism
• Intelligent memory management to reduce hard disk faults on the resume path
• SuperFetch™
• Updated USB hub driver removes serialization delays
• Automatic performance tracing of every suspend, resume transition
• Built on Event Tracing for Windows (ETW)
• New tools to enable partners to test, profile and analyze systems for S3 resume performance

S3 Resume Process Phases

• Power On

• Time to prepare the hardware for resume
• No processor instructions are executed
• Begins with wake event
• E.g., RTC, HW button, wake-capable device
• Ends when processor begins executing instructions
• The performance of the Power On phase can not be measured by software

S3 Resume Process Phases

• BIOS Initialization

• Time required to initialize hardware
• CPU, memory controller, cache, chipset
• Only BIOS code is executing
• Starts with power-on reset vector
• Phase ends when the processor jumps to the OS waking vector
• Phase duration is measured using the processor time-stamp counter (TSC)
• TSC is assumed to be reset (value of 0) during the Power On phase
• Windows records the value of the TSC immediately after OS begins executing instructions
• Windows records the frequency of the TSC during the suspend process

Resume Process Phases

• Device Initialization

• Time required to notify devices that the system has resumed
• Power manger sends IRP_MN_SET_POWER (S0) IRPs to all drivers
• Phase begins immediately after OS regains control from the BIOS
• Phase ends after all drivers have completed their system power (IRP_MN_SET_POWER, S0) IRPs
• Phase duration logged
• IRP start, completion times also recorded

Resume Process Phases

• USER Initialization

• USER applications and services are notified that the system has resumed
• WM_POWERBROADCAST message, PBT_APMRESUME event
• Begins immediately after devices have been initialized
• Ends after the power manager has asked the USER subsystem to notify applications
• USER notifications occur asynchronously from the power manager’s point of view
• USER notifications continue to occur after the power manager has considered resume to be complete
• Phase progress logged

Measuring Resume Performance

• Microsoft measures total S3 resume time as

• BIOS Initialization + Device Initialization phase durations

• Starts when the CPU begins execution

• Ends after all driver IRP_MN_SET_POWER (S0) IRPs have been completed

• This is the benchmark used for the Windows Hardware Logo Requirement

• Logo program requires S3 resume in less than 2000 milliseconds

Resume Performance Best Practices

• It is expected that not all device-specific re-initialization will be complete within the total resume time

• Devices should initialize their hardware when handling their device power (IRP_MN_SET_POWER, D0) IRPs
• Depending on parallelism, this may occur after Device Initialization phase has completed

Resume Performance Best Practices

• Drivers for devices without children devices will help decrease total DriverInit time by completing their S-IRP immediately

• Request a D0 set-power IRP immediately after receiving an S0 set-power IRP
• Complete the S0 set-power IRP immediately
• Do not wait for the D0 IRP completion before completing the S0 IRP
• Continue to queue I/O until the D0 IRP is completed
• Complete any device initialization required when the D0 set-power IRP is received
• Complete the D0 set-power IRP
• Begin handling any queued I/O requests
• I/O should be queued when the Dx set-power IRP is received on the suspend path

• Completing the S-IRP immediately enables the power manager to power up additional devices

Resume Performance Best Practices

• Drivers must not block forward progress of the system on the S3 resume path

• Prevents the power manager from powering up other devices

• Guidelines

• Do not execute a single DPC for more than 100us
• Do not call KeStallExecutionProcessor() for more than 100us total in a single DPC
• If you need additional time to power up your device, use a dedicated thread or a kernel-mode worker thread
• Then, use KeDelayExecutionThread() to wait on hardware
• These are the same guidelines for supporting glitch-free multimedia on Windows Vista
• http://www.microsoft.com/whdc/driver/perform/mmdrv.mspx

Resume Performance Tools

• Resume performance can be measured using PwrTest

• Command-line tool, supports multiple power management scenarios
• Included in the Windows Driver Kit (WDK)
• System can be repetitively cycled through sleep states
• Resume performance information logged to XML file
• Used to profile the system for the Windows Hardware Logo Requirement

• WDK also includes a sample resume performance script

• Cycles through four S3 transitions, ignores the first

• Resume Performance can be observed in the Windows Event Log

• See backup slide for details

Measuring S3 Resume Performance with PwrTest

Summary

• Windows Vista power management goal is simplicity for users

• Windows Vista enables integration of custom power management features with power policy

• Powercfg command-line tool can be used to customize power policy for factory floor scenarios

• Systems with Windows Vista will offer users near-instantaneous S3 resume performance

• S3 resume performance can be measured using PwrTest WDK tool or Windows Event Log

Call To Action

• Test your application, service or driver with Windows Vista power management

• Use PwrTest in WDK

• Support Hybrid Sleep in your driver for a wake-capable device

• Use powercfg command-line tool to configure power policy

• Measure S3 resume performance with PwrTest or the Windows Event Log

• Optimize device drivers for S3 resume performance

Additional Resources

• Power Management and ACPI on Windows Hardware and Driver Central

• http://www.microsoft.com/whdc/system/pnppwr/powermgmt/default.mspx

• White papers

• Measuring Resume Performance on Windows Vista
• http://go.microsoft.com/fwlink/?LinkId=61994
• Direct Application Launch for System Startup on Windows Vista
• http://www.microsoft.com/whdc/system/vista/DirAppLaunch.mspx

• Other WinHEC Sessions

• CPA013: “Case Study: ATI Device Power Management in Windows Vista”
• CPA002: “ACPI in Windows Vista”

Backup Slides Resume Performance Event

• Windows Vista exposes resume performance information in the event log

• Automatically, every sleep/resume transition

• Event details

• Source
• Microsoft-Windows-Power-Troubleshooter
• Event ID
• 1
• Description
• “The system has resumed from sleep”
• Sleep Time: [date-time]
• Wake Time: [date-time]
• Wake source: [wake source description]
• Resume performance, sleep state, Hibernate metrics included in event data

Backup Slides Hybrid Sleep

• Drivers for wake-capable devices may need to do extra work on a Hybrid Sleep transition

• Only necessary if your device supports wake from S3, but not wake from S4
• If your device supports wake from S3, it should also support wake from Hybrid Sleep
• However, IRP_MN_SET_POWER Parameters.Power.State == PowerSystemHibernate (S4) for Hybrid Sleep
• Use the SystemContext field of the IRP_MN_SET_POWER IRP to determine if the system is transitioning to Hybrid Sleep
• Arm for wake if your device supports wake from S3
• Use SYSTEM_POWER_STATE_CONTEXT
• TargetState == PowerSystemSleeping3
• EffectiveState == PowerSystemHibernate

Backup Slides Hybrid Sleep

• Arm device for wake on Hybrid Sleep transition

• TargetSystemState == PowerSystemSleeping3
• EffectiveSystemState == PowerSystemHibernate