Windows 7 Power Management

[darshit]

Microsoft recently released a new 14-page whitepaper entitled “Windows 7 Power Management” to outline the power management technologies in Windows 7 that reduce power consumption.

Power management is one of the aspects of the Windows client and server operating systems that are evolving from Vista and Windows Server 2008 to Windows 7 and Widows Server 2008 R2. Power management tasks allow the operating system, in conjunction with the hardware available, to strike an equilibrium between performance and the resources consumed. On laptops for example this translates into as much battery life as possible. According to Microsoft, the vision is to have Windows as the most energy-efficient computing platform independent of the hardware configuration or software workloads.

The list of improvements contains the following topics:

• Reduced Power Consumption
• Idle Resource Utilization
• Trigger Start Services
• Enhanced Processor Power Management
• Timer Coalescing
• Device Power Management
• Adaptive Display Brightness
• Low-Power Audio
• Bluetooth Power Improvements
• Networking Power Improvements
• Enhanced User Experiences
• Greater Enterprise Power Management
• Power Efficiency Diagnostics
• Group Policy
• Windows Management Instrumentation
• Power Policy

[darshit]

Some Points in 14-page whitepaper “Windows 7 Power Management” are as follows:


Reduced Power Consumption

Microsoft designed Windows 7 with a strong focus on reducing the overall power consumption by investing in key areas of the platform including performance optimizations, idle resource utilization, device power management, and key end-user scenarios. Energy efficiency requires investments across the entire platform, not only in the core hardware or in the operating system. While Windows 7 can have a significant impact on platform energy efficiency, attached devices, and non-Microsoft and end-user applications, other platform extensions often have a larger total impact. The complexity and quantity of platform extensions require a broad approach to energy efficiency beyond focusing on a single component in the platform. In addition to core investments in Windows 7, Microsoft has emphasized ecosystem engagements for energy efficiency. Ecosystem partners, including IT pros, may leverage Windows 7 technical documentation, built-in diagnostic tools, and rich performance analysis tools to help identify issues across the enterprise.

Idle Resource Utilization

Idle efficiency is critical for the overall battery life of a PC because idle time dominates most scenarios. Reducing idle power consumption reduces the base power consumption. For example, if a portable computer uses 12 watts when the system is idle, all other scenarios increase power by some amount over the base 12 watts. Reducing idle power consumption benefits all other end-user workloads and scenarios, from DVD playback to office productivity. Reducing idle power consumption can be achieved by reducing the resource utilization of the system when it is idle. It can also be achieved by enabling the hardware to go into lower power states during long periods of inactivity. Resource utilization includes the processor, disk, memory, and network activity on the system. Windows 7 helps improve efficiency by reducing resource utilization when the system is idle. Reducing processor activity is particularly critical because of the large dynamic range of power consumption in modern processors. The typical portable computer processor consumes nearly 0 watts when idle, but it can consume up to 35 watts when fully utilized.

Windows 7 provides greater idle efficiency by reducing (and in many cases eliminating) background activity on the system. Where periodic activity cannot be eliminated because of strict polling requirements (such as timers on the USB stack), Windows 7 exposes a new timer coalescing feature. (For more information, see ―Timer Coalescing API later in this document). Timer Coalescing allows Windows 7 to align various background activities and execute them at the same time to keep the processor idle for longer periods of time. Additionally, Windows 7 defers non-critical background activity when the system is on battery power to help extend the battery life of a portable computer.

Trigger Start Services

System services often start automatically, run in the background, and wait for infrequent events to occur. Windows 7 can reduce background activities by trigger-starting system services, which starts background processes only when a specific event occurs. Events like device insertion and IP address changes can trigger-start services. For example, in Windows 7 the Windows Bluetooth service only starts when a Bluetooth device is attached to the computer.

Idle processors help reduce power consumption, allowing users to benefit from longer battery life. By reducing the number of background services running, Windows 7 helps improve energy efficiency and computer responsiveness. IT pros can take advantage of this capability by enabling trigger-starting for services that are part of their enterprise image, and they can validate performance impacts with the Windows Performance Tool Kit (XPerf) (http://go.microsoft.com/fwlink/?LinkId=147988).
For more information regarding the Windows service improvements in Windows 7, see the paper ―Developing Efficient Background Processes for Windows (http://go.microsoft.com/fwlink/?LinkId=147990).

Enhanced Processor Power Management

Windows 7 includes device driver support for the latest processor power management (PPM) technologies. Performance and power consumption modes for the processor are called performance states. The PPM technologies allow the operating system to choose the right processor performance state depending on the load, and then scale the performance of the system accordingly. Windows 7 features significant changes to the accounting of processor activity, which enables much greater accuracy in determining which performance state is appropriate for the processor based on current system activity. These improvements enable greater energy efficiency across a broad range of workloads. In-box support of these technologies enables power-saving benefits immediately after installation.

[darshit]

Timer Coalescing

Modern processors are able to reduce their power consumption by taking advantage of the periods of idle time between executing instructions for software activity. However, many PPM technologies require a minimum amount of idle time to obtain a net power-savings benefit. If the processor is idle for very short periods of time, the power required to enter and exit the low-power state can be greater than the power saved. Windows Timer Coalescing can help increase the duration of processor idle periods by combining various software timer expirations. Combining various software timer expirations allows the kernel to execute all of the timer activity on the same timer interrupt, which enables longer periods of idle time on each processor by waking up several timers concurrently and doing the work together. When the work is complete, the processor is able to return to a deep idle state for an extended period of time. Windows 7 provides new application programmer interfaces (APIs) for driver developers and for application and service developers to take advantage of Windows Timer Coalescing.

Device Power Management

Windows 7 provides enhanced device power management. It enables low-power modes across several technologies, including Adaptive Display Brightness, Smart Network Power, and other device classes. The following sections describe these improvements.

Adaptive Display Brightness

On today’s mobile platforms, the display is a significant part of the overall system power usage—up to 40 percent. Previous versions of the Windows operating system include power policy settings to turn off the display after a period of inactivity and lower power consumption. The display is typically powered down after 10–15 minutes of user inactivity. However, there may be many periods of user inactivity that are shorter than the display-off power policy. These short periods of user inactivity occur frequently throughout the day.

Adaptive Display Brightness defines additional power policy settings to dim the display after a period of inactivity. Dimming the display can help reduce the display power consumption, although not as much as turning off the display. Adaptive Display Brightness also supports hardware Ambient Light Sensor (ALS) devices to automatically adjust display brightness to the surrounding ambient light, even when the user is interacting with the system.

Low-Power Audio

Windows 7 supports the latest Intel HD Audio low-power specification. This specification introduces a fourth power state—D3Cold—which is defined as the lowest unresponsive power state that a codec can go into yet still wake up. The Windows 7 HD Audio Class Driver takes advantage of this power state to further conserve power when an audio device is not in use. Windows 7 also supports USB audio-class selective suspend, which reduces the complexity of platform integration for array microphone and USB Web camera solutions. Support for selective suspend in audio-class devices helps make USB-based solutions possible without significantly affecting battery life.

Bluetooth Power Improvements

Windows 7 helps increase battery life by enabling state of selective suspend when it detects that a Bluetooth device has entered a lower-power state. Typically, when the client computer is connected to a Bluetooth device, the radio and the USB bus are always active, whereas the device may be entering a lower-power state if it does not need to use the Bluetooth connection. With Windows 7, if the device enters its low-power (or ―sniff‖) mode, Windows 7 enables a state of selective suspend on the computer, allowing both sides of the connection to save power.


Networking Power Improvements

Windows 7 provides new power management features for wired and wireless networking technologies. In Windows 7, when users disconnect the network cable, Windows 7 can automatically place the network adapter into a lower-power state known as D3. (D3 is only available when the adapters and drivers support this power state.) This provides an additional power savings of as much as 0.5 watts. These results will vary depending on the hardware configuration and network controller. When the user reconnects the network cable, Windows 7 automatically places the network adapter in the full-power state, known as D0. Windows 7 enables wireless network controllers to enter low-power modes. This capability is configurable through power policy settings. Although this functionality was available in the Windows Vista operating system, many wireless access points did not correctly support low-power modes, which caused the computer to suddenly disconnect from the wireless network. In Windows 7, the networking driver stack queries the access point for low-power capabilities and enters the low-power mode only if the access point supports it. This arrangement allows the default power policy setting to be configured for

[darshit]

For More Details Download this 14-page whitepaper “Windows 7 Power Management”