Difference between revisions of "Power saving"

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(USB Autosuspend: merge from Laptop)
m (Backlight: provide link to Backlight)
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SUBSYSTEM=="backlight", ACTION=="add", KERNEL=="acpi_video0", ATTR{brightness}="1"
SUBSYSTEM=="backlight", ACTION=="add", KERNEL=="acpi_video0", ATTR{brightness}="1"
See [[Backlight]] for more information.
=== Bluetooth ===
=== Bluetooth ===

Revision as of 14:15, 26 June 2013

Template:Article summary start Template:Article summary text Template:Article summary heading Template:Article summary wiki Template:Article summary wiki Template:Article summary wiki Template:Article summary wiki Template:Article summary wiki Template:Article summary end This article covers the configuration needed to turn on power saving features. Almost all of the features listed here are worth using whether or not the computer is on AC or battery power. Most have negligible performance impact and are just not enabled by default because of commonly broken hardware/drivers. Reducing power usage means reducing heat, which can even lead to higher performance on a modern Intel or AMD CPU, thanks to dynamic overclocking.


If you would like to create your own scripts and power saving settings such as by udev rules you can take the following settings as a reference.


By default, audio power saving is turned off by most drivers. It can be enabled by setting the power_save parameter; a time (in seconds) to go into idle mode. To idle the audio card after one second, create

options snd_hda_intel power_save=1

for Intel, or use

 options snd_ac97_codec power_save=1

for ac97.

Note: Toggling the audio card's power state can cause a popping sound or noticeable latency on some broken hardware.

Active state power management

To verify that ASPM is enabled:

$ cat /sys/module/pcie_aspm/parameters/policy
[default] performance powersave

Either [default] or [powersave] means you do not need to force it on. Otherwise, it's either unsupported or broken on your hardware, or has to be forced on with pcie_aspm=force on the kernel line.

  • Forcing on ASPM can cause a freeze/panic, so make sure you have a way to undo the option if it doesn't work.
  • On systems that don't support it forcing on ASPM can even increase power consumption.


When system starts, screen backlight is set to maximum by default. This can be fixed by specifying backlight level in the following udev rule:

SUBSYSTEM=="backlight", ACTION=="add", KERNEL=="acpi_video0", ATTR{brightness}="1"

See Backlight for more information.


Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: The device should likely be disabled with hciconfig first. (Discuss in Talk:Power saving#)
Blacklist the hci_usb module if the driver is loaded automatically.

Alternatively, blacklist the btusb and bluetooth modules.

Another variant is to rfkill it:

# rfkill block bluetooth

Or with udev rule:

SUBSYSTEM=="rfkill", ATTR{type}=="bluetooth", ATTR{state}="0"


If you won't use integrated web camera then blacklist the uvcvideo module.

Kernel parameters

This section uses configs in /etc/sysctl.d/, which is "a drop-in directory for kernel sysctl parameters, extending what you can already do with /etc/sysctl.conf." See The New Configuration Files and more specifically systemd's sysctl.d man page for more information.

Disabling NMI watchdog

The NMI watchdog is a debugging feature to catch hardware hangs and cause a kernel panic. On some systems it can generate a lot of interrupts, causing a noticeable increase in power usage.

kernel.nmi_watchdog = 0

or add nmi_watchdog=0 to the kernel line to disable it completely from early boot.

Writeback Time

Increasing the VM dirty writeback time can help to aggregate I/O together - reducing disk writes, and decreasing power usage:

 vm.dirty_writeback_centisecs = 1500

To do the same for journal commits with ext4 and some other filesystems, use commit=15 as a parameter in fstab or with the rootflags kernel parameter.

Laptop Mode

See the kernel documentation on the laptop mode 'knob.' "A sensible value for the knob is 5 seconds."

 vm.laptop_mode = 5

Network interfaces

Wake-on-LAN can be a useful feature, but if you're not making use of it then it's simply draining extra power waiting for a magic packet while in suspend. Disabling for all Ethernet interfaces:

ACTION=="add", SUBSYSTEM=="net", KERNEL=="eth*" RUN+="/usr/bin/ethtool -s %k wol d"

To enable powersaving on all wireless interfaces:

ACTION=="add", SUBSYSTEM=="net", KERNEL=="wlan*" RUN+="/usr/bin/iw dev %k set power_save on"

In these examples, %k is a specifier for the kernel name of the matched device. For example, if it finds that the rule is applicable to wlan0, the %k specifier will be replaced with wlan0. To apply the rules to only a particular interface, just replace the pattern eth* and specifier %k with the desired interface name. For more information, see Writing udev rules.

In this case, the name of the configuration file is important. Due to the introduction of persistent device names via 80-net-name-slot.rules in systemd v197, it is important that the network powersave rules are named lexicographically before 80-net-name-slot.rules, so that they are applied before the devices are named e.g. enp2s0.

PCI Runtime Power Management

ACTION=="add", SUBSYSTEM=="pci", ATTR{power/control}="auto"

SATA Active Link Power Management

Note: This adds latency when accessing a drive that has been idle, so it's one of the few settings that may be worth toggling based on whether you're on AC power.
SUBSYSTEM=="scsi_host", KERNEL=="host*", ATTR{link_power_management_policy}="min_power"

USB Autosuspend

To enable USB autosuspend after 2 seconds of inactivity:

ACTION=="add", SUBSYSTEM=="usb", TEST=="power/control" ATTR{power/control}="auto"
ACTION=="add", SUBSYSTEM=="usb", TEST=="power/autosuspend" ATTR{power/autosuspend}="2"

Other option is to use modprobe:

options usbcore autosuspend=2

Device Power Management

Tango-inaccurate.pngThe factual accuracy of this article or section is disputed.Tango-inaccurate.png

Reason: Should be done with a udev rule. (Discuss in Talk:Power saving#)
echo auto | tee /sys/bus/i2c/devices/*/power/control > /dev/null
echo auto | tee /sys/bus/spi/devices/*/power/control > /dev/null

Tools and scripts


There are many scripts and tools which make use of the various settings described in the previous sections. These are notably:

If you do not want to take care of the settings by yourself it is recommended to use these tools. But be aware of running only one of these tools to avoid possible conflicts as they all work more or less similar.

Print power settings

This script prints power settings and a variety of other properties for USB and PCI devices. Note that root permissions are needed to see all settings.


for i in $(find /sys/devices -name "bMaxPower")
	title=$(lsusb -s $busnum:$devnum)

	printf "\n\n+++ %s\n  -%s\n" "$title" "$busdir"

	for ff in $(find $busdir/power -type f ! -empty 2>/dev/null)
		v=$(cat $ff 2>/dev/null|tr -d "\n")
		[[ ${#v} -gt 0 ]] && echo -e " ${ff##*/}=$v";
	done | sort -g;

printf "\n\n\n+++ %s\n" "Kernel Modules"
for mod in $(lspci -k | sed -n '/in use:/s,^.*: ,,p' | sort -u)
	echo "+ $mod";
	systool -v -m $mod 2> /dev/null | sed -n "/Parameters:/,/^$/p";