Power saving
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.
Contents
- 1 Ready to run scripts
- 2 Custom settings
- 2.1 Audio
- 2.2 Active State Power Management
- 2.3 Backlight
- 2.4 Bluetooth
- 2.5 Web-Camera
- 2.6 Disabling NMI watchdog
- 2.7 Disabling Wake-on-LAN
- 2.8 PCI Runtime Power Management
- 2.9 Wireless power saving
- 2.10 Writeback Time
- 2.11 Laptop Mode
- 2.12 SATA Active Link Powermanagement
- 2.13 USB Autosuspend
- 2.14 Device Power Management
- 2.15 View Power Setings
- 2.16 See also
Ready to run scripts
There are already a couple of scripts and tools which make use of the various settings described in the next section. 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.
Custom settings
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.
Audio
By default, audio power saving is turned off by most drivers. It can be enabled by setting the power_save parameter to a time (in seconds) to go in idle.
- Intel
/etc/modprobe.d/audio_power_save.conf
options snd_hda_intel power_save=1
- ac97
/etc/modprobe.d/audio_power_save.conf
options snd_ac97_codec power_save=1
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/broken on your hardware, or has to be forced on with pcie_aspm=force
on the kernel line.
Backlight
When system starts, screen backlight is set to maximum by default. This can be fixed by specifying backlight level in the following udev rule:
/etc/udev/rules.d/backlight.rules
## SET BACKLIGHT SUBSYSTEM=="backlight", ACTION=="add", KERNEL=="acpi_video0", ATTR{brightness}="1"
Bluetooth
Blacklist thehci_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:
/etc/udev/rules.d/bt.rules
## DISABLE BLUETOOTH SUBSYSTEM=="rfkill", ATTR{type}=="bluetooth", ATTR{state}="0"
Web-Camera
If you won't use integrated web camera then blacklist the uvcvideo
module.
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.
/etc/sysctl.d/disable_watchdog.conf
kernel.nmi_watchdog = 0
or add nmi_watchdog=0
as a kernel parameter to disable it completely from early boot.
Disabling Wake-on-LAN
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:
/etc/udev/rules.d/disable_wol.rules
ACTION=="add", SUBSYSTEM=="net", KERNEL=="eth*" RUN+="/usr/sbin/ethtool -s %k wol d"
You can use multiple names in the matches; for example, KERNEL=="lan0|eth*"
eth*
names are not static.PCI Runtime Power Management
/etc/udev/rules.d/pci_pm.rules
ACTION=="add", SUBSYSTEM=="pci", ATTR{power/control}="auto"
Wireless power saving
Enabling for a specific interface:
/etc/udev/rules.d/wlan0_power_save.rules
ACTION=="add", SUBSYSTEM=="net", KERNEL=="wifi0" RUN+="/usr/sbin/iw dev wifi0 set power_save on"
Enabling for all interfaces:
/etc/udev/rules.d/wifi_power_save.rules
ACTION=="add", SUBSYSTEM=="net", KERNEL=="wlan*" RUN+="/usr/sbin/iw dev %k set power_save on"
Writeback Time
Increasing the VM dirty writeback time can help to aggregate I/O together - reducing disk writes, and decreasing power usage:
/etc/sysctl.d/dirty_writeback.conf
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
/etc/sysctl.d/laptop_mode.conf
vm.laptop_mode = 5
SATA Active Link Powermanagement
/etc/udev/rules.d/hd_power_save.rules
SUBSYSTEM=="scsi_host", KERNEL=="host*", ATTR{link_power_management_policy}="min_power"
USB Autosuspend
To enable USB autosuspend after 2 seconds of inactivity:
/etc/udev/rules.d/usb_power_save.rules
ACTION=="add", SUBSYSTEM=="usb", TEST=="power/control" ATTR{power/control}="auto" ACTION=="add", SUBSYSTEM=="usb", TEST=="power/autosuspend" ATTR{power/autosuspend}="2"
Device Power Management
echo auto | tee /sys/bus/i2c/devices/*/power/control > /dev/null echo auto | tee /sys/bus/spi/devices/*/power/control > /dev/null
View Power Setings
This function shows various power settings. Note you either must be root or you must have sudo.
function aa_power_settings () { sudo bash -c ' for i in `find /sys/devices -name "bMaxPower"`; do for ii in `find $i -type f`; do bd=`dirname $ii`; busnum=`cat $bd/busnum`; devnum=`cat $bd/devnum`; title=`lsusb -s $busnum:$devnum`; echo -e "\n\n+++ $title\n -$bd\n -$ii"; for ff in `find $bd/power -type f ! -empty 2>/dev/null`; do v=`cat $ff 2>/dev/null|tr -d "\n"`; [[ ${#v} -gt 0 ]] && echo -e " `basename $ff`=$v"; v=; done | sort -g; done; done; echo -e "\n\n\n+++ Kernel Modules\n"; for m in `command lspci -k|sed -n "/in use:/s,^.*: ,,p"|sort -u`; do echo "+ $m"; systool -v -m $m 2> /dev/null | sed -n "/Parameters:/,/^$/p"; done '; }