Power Management

Power management provides the ability to control and manage the electrical power usage of a computer system or device. Power management enables systems to conserve energy by using less power when idle and by shutting down completely when not in use. For example, desktop computer systems can use a significant amount of power, and often (particularly at night) are left idle. Power management software can detect that the system is not being used and power it or some of its components down.

This chapter provides information on the following subjects:

• Power Management Framework

• Device Power Management Model

• System Power Management Model

• Power Management Device Access Example

• Power Management Flow of Control

Power Management Framework

The Solaris Power Management framework depends on device drivers to implement device-specific power management functionality. The framework is implemented in two parts:

• Device power management - Automatically turns off unused devices to reduce power consumption

• System power management - Automatically turns off the computer when the entire system is idle

Device Power Management

The framework allows devices to reduce their energy consumption after a specified idle time interval. To perform effective device power management, system software monitors the different devices and determines when they are not in use. Since only device drivers are able to determine when a device is idle, and only device drivers are able to reduce power consumption of a device, the Power Management framework exports interfaces to enable communication between the system software and the device driver.

The Solaris Power Management framework provides the following:

• A device-independent model for power-manageable devices.

• dtpower(1M), a graphical user interface for workstation power management. (Power management can also be implemented through the power.conf(4) and /etc/default/power files.)

• A set of DDI interfaces for the device driver to notify the framework if the device can be power managed, and when it is idle or busy.

System Power Management

System power management consists of turning off the entire computer after saving its state so that it can be returned to the same state immediately when it is turned back on.

To shut down an entire system and later return it to the state it was in prior to the shutdown:

• Stop (and later restart) kernel threads and user processes.

• Save the hardware state of all devices on the system to disk (and later restore it).

SPARC only - System power management is currently implemented only on some SPARC systems supported by the Solaris 9 operating environment.

The Solaris operating environment System Power Management framework provides the following:

• A platform-independent model of system idleness

• dtpower(1M), a graphical user interface for workstation power management. (Power management can also be implemented through thepower.conf(4) and /etc/default/power files.)

• A set of interfaces for the device driver to override the method for determining which drivers have hardware state

• A set of interfaces to allow the framework to call into the driver to save and restore the device state

• A mechanism for notifying processes that a resume operation has occurred

Device Power Management Model

The following sections describe the details of the device power management model. This model includes the following elements:

• Components

• Idleness

• Power levels

• Dependency

• Policy

• Device power management interfaces

• Power management entry points