Advanced Power Management for Linux operating systems

In Windows, we are very familiar with system power management. We can use the advanced power management module of the motherboard to implement functions such as STR and STD. For laptop users, it is more important to use advanced power management to sleep their laptop and save battery resources. The above mentioned functions are implemented on Windows platforms, which may no longer be difficult for us. However, I am afraid few will know about it if I change to Linux. Today we will introduce the implementation of power management in Linux. Since many servers use Linux, the importance of power management becomes very obvious.

There are two Power Management methods in x86 machines: APM (Advanced Power Management, Advanced Power Management) and ACPI (Advanced Configuration and Power Interface, Advanced Configuration and Power Interface ). APM is the old standard, while ACPI provides more flexible interfaces for managing computers and devices. Linux supports these two protocols, but sometimes manual configuration is required. In addition, the two standards cannot run simultaneously. By default, Linux runs ACPI.

APM allows you to put the machine in the Suspend or Standby status and check the battery capacity. ACPI also allows you to independently power off peripherals (such as display, video card, and PCI Bus), giving you more control over power saving. To make the power management function take effect, you need to enable it in the BIOS and Linux core, and load the necessary application software in linux.

Check whether the system supports Power Management

In the newer core, all include the Support for ACPI and APM. Generally, ACPI is activated. Use dmesg to check whether:

Dmesg | egrep-I '(apm | acpi )'

Kernel command line: vga = 274 quiet console = ttyS3, 9600 acpi = no-idleoot =/dev/hda3

ACPI: Core Subsystem version [1, 20010208]

ACPI: Subsystem enabled

ACPI: System firmware supports: C2

ACPI: plvl2lat = 99 plvl3lat = 1001.

ACPI: C2 enter= 1417 C2 exit = 354

ACPI: C3 enter =-1 C3 exit =-1

ACPI: Not using ACPI idle

ACPI: System firmware supports: S0 S1 S4 S5

In addition, the/proc/sys/ACPI directory will be added to systems that support acpi. If it exists, it indicates that the core has loaded the ACPI driver.

Specific Application Instance

We recommend that you use the latest core (for example, 2.4.5 ). Because the old core supports less features, while 2.2.x supports ACPI at the core, there are only a few features.

1. Advanced Power Management

APM applications include apmd and other applications (such as APM ). We recommend that you go to rpmfind.net to find the latest version suitable for your use. After installing and running OK, we can test the APM command.

The simplest use of APM is to display the battery capacity on the machine.

APM

AC on-line, no system battery

If APM is not supported, "No APM support in core" is displayed ". Check whether/proc/apm exists. If not, check whether the core after APM installation is running. If you use APM as a module, check whether the module is loaded. Apm can also use-S/-s to enter the Standby and Suspend statuses.

Figure 1

Figure 1 shows the KDE System interface, which uses APM to check the battery capacity and manages the energy-saving mode of other hardware (Figure 2) and displays it on the taskbar. For more information, visit www.linuxdoc.org.

2. ACPI

Linux provides better support for ACPI and more related documents than APM.

ACPI's authoritative website is.

Figure 2

The Pmtools command is Pmtest, which allows you to detect devices. Generally, it shows the ACPI devices in your system and allows you to "Suspend" or "Back up" them. It must run with root.

/Pmtools/pmtest

VGA (D0)

Keyboard (D0)

PCI 0 × 0 (D0)

System 0 × 0 (D0)

It seems that VGA monitors, keyboards, PCI buses, and systems are all recognized as ACPI devices. Their statuses are D0, which is the active state. We can set the status to D1/D2 (minimizing power consumption) or D3 (completely off ). For example:

/Pmtools/pmtest-d1 VGA

The display should be black now. This does not cause the video card to stop generating a video signal (the display also indicates an input signal), but only converts all the signals to black. /Pmtools/pmtest-d0 VGA can be restored.

The above is just a few examples. You can take the opposite steps to manage your system and give full play to the advanced voltage management function.