About how to troubleshoot power plans in Windows 7

Overview

The following three main power plans are available in Windows 7:

• High performance
• Balanced
• Power saver

Each power plan targets different uses, and you can easily switch between different power plans to provide tradeoffs between performance and power consumption. By default, the Balanced power plan is recommended, because it configures Windows 7 to dynamically scale the level of delivered performance, depending on current workload requirements. The Power saver power plan is designed for maximizing energy savings and is good for mobile PC usage and for maximizing battery life. (A mobile PC is a notebook, laptop, or other portable computer that runs Windows Vista or a later version of Windows.) The High performance power plan disables dynamic scaling of performance to match the workload and instead delivers constant high performance levels at the cost of increased power consumption. This power plan is useful in certain scenarios that are highly performance or latency sensitive or in scenarios in which power consumption is not an issue.

Power plans can be customized. You can use each plan as a template to configure your own unique power plan that meets your needs. If battery life is your key concern but you want a bright display, you should create a power plan based on the Power saver power plan. After you create a power plan, you can use the Change Advanced Power Settings feature to better adjust the plan to meet your needs. For example, you can now change the display brightness to a comfortable level. Be aware that changing the default setting will affect power consumption and performance, depending on the setting. Increasing the display brightness will result in increased power consumption.

By default, the option to change a power plan is disabled. To enable this option, click Change plan settings, click Change advanced power settings, and then click Change settings that are currently unavailable. This may increase the number of options that you can adjust.

Where does the power go?

• On a large mobile PC that has a 21-inch LCD screen, we found that the display consumed as much as 43 percent of the total power being consumed at high resolutions. This was especially true when the mobile PC was combined with a high-end graphics card that was tasked with video editing or gaming. An external display can consume from several watts of power to several hundred watts of power for a large plasma, LCD, or projected screen when you use Windows 7 Media Center. Newer OLED displays are on the horizon and will have a significant reduction in power consumption.
• Sustained hard disk usage consumes an average of around 5 percent of total power consumption in a mobile PC. New solid-state drives are much more efficient, because there is no mechanical mechanism and there are no platters spinning. Hybrid drives that have a solid-state and disk combo are an excellent choice. Another bonus to having no moving parts is that the hard disk is more resistant to the bumps and harsher treatment that mobile PCs experience. For servers, a datacenter-grade hard disk consumes on average 10 watts of power while in the idle state. When you multiply that by 1,000 or more hard disks in a typical datacenter, you have high current loads and additional cooling needs.
• More RAM requires more power, because the chips are all powered on when you start a computer regardless of whether it has data.
• In terms of the total power being consumed to keep a system running, chipsets can on average consume 21 percent of the power, whereas processors (depending on the number and speed of the processors) can consume 10 percent of the power. Network adapters can consume 4 percent of the power, whereas wireless NICs may require more power. Typically, enterprise-level NICs that run in the gigabytes consume even more power.
• The PC bus can also consume power. However, newer motherboards let buses be powered down when they are not being tasked. Or, you can set your system to Passive Cooling. Some manufacturers expose a great number of features that can be changed in the BIOS. Not all BIOSes expose or take advantage of these features. Some BIOSes may have these features but do not let the operating system alter the settings from the BIOS.
• Attached devices such as mobile phones, TV cards, MP3 players, GPS devices, and wireless NICs all take additional amounts of power. When you attach these devices, the bus to which they are connected is powered up. Additionally, these devices may start charging their own battery. If you are using an AC power source, that is fine. But if you are using battery power or are using one or more devices that may not support the Selective Suspend feature when they run on battery, the battery run time will decrease significantly.
• Drivers, services, applications, and devices can add significant demands on the battery, and any combination of them can affect battery life by 20 to 30 percent or more.

Power Plans

High performance

The High performance power plan maximizes the brightness level and can increase the computer's performance. The tradeoff is reduced battery life and more heat generation because of more power use by the CPU, by the LCD, and by devices. The CPU fan will run faster and more frequently. This power plan is great for the prompt response that you want for gaming or for video editing. Opportunity cost is a key issue with customers. The High performance power plan requires more power per transaction, increases heat generation, and puts increased demand on moving parts such as fans.

Advantages

• The display is brighter. (This is helpful for outside use.)
• The computer operates at a very high level of performance.

Disadvantages

• There is the potential for more heat generation.
• Processor performance is not optimized during short idle periods.
• The CPU fan spins up more frequently.

Balanced

The Balanced power plan scales the performance level to match the current workload. This plan provides an optimal tradeoff between power consumption and performance on mobile PCs and on desktops and is the default setting.

Power saver

The Power saver power plan saves power by reducing system performance and screen brightness.

Advantages

• Battery life increases because of reduced power level.
• Screen brightness is reduced automatically.
• The CPU and hardware are set to aggressively take advantage of downtime.
• A mobile PC or a desktop computer consumes less power and generates less heat.

Disadvantages

• Applications may run slower or start slower.
• The screen may not be bright enough for outside use.

Troubleshooting

PowerCFG

PowerCFG is a powerful command-line tool that helps in diagnosing power-management issues. Frequently, a user may prefer not to wake the computer by using the mouse or is not sure why a computer woke. You can disable and enable devices by using the PowerCFG tool. Or, you can use the Power Management tab in the properties of the device in Device Manager to select the Allow this device to wake the computer check box. Additionally, the PowerCFG tool can be scripted for domain use.

The following are the more common commands that can be used to identify sleep states and default settings:

• POWERCFG -L or POWERCFG -LIST
  
  Use this command first. This command lists all power plans in the current user's environment. The power plan that is listed with the asterisk (*) is the active power plan.
• POWERCFG -Q or POWERCFG -QUERY
  
  Use this command second. Then, you can determine the exact settings that are applied. This command lists the contents of the power plans. To redirect the listing to a file, use a command that resembles the following:
  Powercfg -Q >c:\test.txt
• POWERCFG -DEVICEQUERY wake_armed
  
  Use this command to determine the devices that are set so that the user can wake the computer.
  
  For a mobile PC, this command may show devices similar to the following:
  • Standard 101/102-Key
  • Microsoft Natural PS/2 Keyboard with HP QLB
  • Synaptics PS/2 Port TouchPad
  
  For a desktop computer, this command may show devices similar to the following:
  • HID-compliant mouse (002)
  • Broadcom NetXtreme Gigabit Ethernet
  • HID Keyboard Device (002)

For more information about the PowerCFG options, run the POWERCFG /? command. Or, visit the following Microsoft TechNet website:

Tips for troubleshooting

The following are tips that you have to consider when you troubleshoot power plans in Windows 7:

• What is the purpose of the computer? Is this a mobile PC that experiences little high-end use? Is it a datacenter-class server that has mission-critical SQL installed? Or, is it something in between?
• Does the computer have the latest BIOS installed? This is important when you investigate power issues.
• What are the BIOS settings that are available? Examine the BIOS options. Frequently, a user may have changed settings that affect the operating system. OEMs may expose the _OSC ACPI method to enable an operating system to adjust BIOS settings. For example, the DC mode for a mobile PC may set the CPU performance P-STATE level. The operating system would be unable to change this if the BIOS vendor did not let the operating system take ownership of this resource. The OEM may also adjust the BIOS and hardware so that regulatory requirements are compliant with set standards. In these cases, changing the settings may not be an option. These settings may not even appear in the Power Management console.
• Have the default settings for the power plan changed? To determine this, use the POWERCFG -Q command. If the default settings are changed, reset the current power plan. Frequently, a user or the system administrator may adjust the power plans. Remember, Group Policy may be enforced; changing a power policy that is controlled by Group Policy lasts only until the user logs on again. An administrator may completely block changes, or items from the list may be removed from use. The administrator should be consulted on these issues, and you must connect as an administrator when you use Remote Desktop to make changes. The key point to remember is that not all power policies are appropriate to all users and to their specific equipment.
• Power plans can be customized by an administrator, by a power application, or by Group Policy. Check these items before you continue to troubleshoot. Before you start any diagnostics or restore the power plans by using the Restore default settings for this plan option, you should capture the current settings by using the POWERCFG –EXPORT command. You can also click Create a power plan and then adjust the customized plan settings. If the power plans become corrupted, you can restore the power plans to default settings. This action will overwrite all default schemes.
  
  To restore the power plans to default settings, follow these steps:
  1. Click Start.
  2. In the Search programs and files box, type cmd.
  3. Right-click CMD, and then click Run as administrator.
  4. At the command prompt, type powercfg -restoredefaultschemes, and then press ENTER.
  5. At the command prompt, type exit to exit the Command Prompt window.
  6. Restart the computer.
• Does the computer have an OEM-supplied power-management application that is installed? If this is the case, look for updates, or test by disabling it. Many times, the OEM may augment the power-management policies by customizing the policies for their specific device. Contact the manufacturer when the power-management application is not working correctly.
• Review Windows Update. The Windows Update service is a key item to review. Also, make sure that you search the Microsoft Knowledge Base for known issues. Windows Update may have updated drivers available that may be relevant to your current issue. Many times, updated drivers are listed in the "Optional" section of Windows Update.

Frequently asked questions

Q1: Why does my computer wake every day at 12:48 and then run a diagnostic tool?

A1: To determine why this occurs, use the -WAKETIMERS option to determine what is currently set. Scheduled tasks are one of the primary items that the -WAKETIMERS option will show. To use this option, run the following command:Note If your computer is from an OEM, the results of this command may resemble the following:

Q2: How can I determine all the available sleep states?

A2: Use the -AVAILABLESLEEPSTATES option. To do this, run the following command:Example 1

The following is an example of the sleep states on a mobile PC from an OEM:
Example 2

The following is an example of a case in which the sleep states are disabled. This example was created by removing the current video driver and by using the VGA driver. The VGA driver does not support sleep states and does not poll the device for supported sleep state support. Windows polls not only the driver but also the BIOS before it enables any sleep states.
Note Do not forget to check the Power Options item in Control Panel and in the computer's BIOS, because available sleep states can be enabled or disabled in these locations.