Difference between revisions of "Power saving"

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[[Category:Power management]]
#REDIRECT [[Power management]]
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 [[Wikipedia:Intel Turbo Boost|dynamic overclocking]].
==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:
* [[TLP]]
* [[Powerdown]]
* {{AUR|powerconf}}
* [[Laptop Mode Tools]]
* [[pm-utils]]
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.
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.
{{Note|Toggling the audio card's power state can cause a popping sound or noticeable latency on some broken hardware.}}
{{hc|/etc/modprobe.d/audio_power_save.conf|2=options snd_hda_intel power_save=1}}
{{hc|/etc/modprobe.d/audio_power_save.conf|2=options snd_ac97_codec power_save=1}}
==Active State Power Management==
To verify that [[Wikipedia:Active State Power Management|ASPM]] is enabled:
{{hc|$ cat /sys/module/pcie_aspm/parameters/policy|[default] performance powersave}}
Either {{ic|[default]}} or {{ic|[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 {{ic|1=pcie_aspm=force}} on the [[kernel line]].
{{Warning|Forcing on ASPM can cause a freeze/panic, so make sure you have a way to undo the option if it doesn't work.}}
{{Warning|On systems that don't support it forcing on ASPM can even increase power consumption.}}
== 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:
SUBSYSTEM=="backlight", ACTION=="add", KERNEL=="acpi_video0", ATTR{brightness}="1"
== Bluetooth ==
{{expansion|reason=The device should likely be disabled with hciconfig first.}}
[[Kernel_modules#Blacklisting|Blacklist]] the {{ic|hci_usb}} module if the driver is loaded automatically.
Alternatively, [[Kernel_modules#Blacklisting|blacklist]] the {{ic|btusb}} and {{ic|bluetooth}} modules.
Another variant is to {{pkg|rfkill}} it:
# rfkill block bluetooth
Or with udev rule:
SUBSYSTEM=="rfkill", ATTR{type}=="bluetooth", ATTR{state}="0"
== Web-Camera ==
If you won't use integrated web camera then [[Kernel_modules#Blacklisting|blacklist]] the {{ic|uvcvideo}} module.
==Disabling NMI watchdog==
The [[Wikipedia:Non-maskable interrupt|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.
{{hc|/etc/sysctl.d/disable_watchdog.conf|2=kernel.nmi_watchdog = 0}}
or add {{ic|1=nmi_watchdog=0}} as a [[kernel parameter]] to disable it completely from early boot.
==Disabling Wake-on-LAN==
[[Wikipedia: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:
{{hc|/etc/udev/rules.d/disable_wol.rules|2=ACTION=="add", SUBSYSTEM=="net", KERNEL=="eth*" RUN+="/usr/bin/ethtool -s %k wol d"}}
You can use multiple names in the matches; for example, {{ic|1=KERNEL=="lan0&#124;eth*"}}
{{Note|This should be combined with [[udev#Network device|static naming]] of devices, the {{ic|eth*}} names are not static.}}
== PCI Runtime Power Management ==
{{hc|/etc/udev/rules.d/pci_pm.rules|2=ACTION=="add", SUBSYSTEM=="pci", ATTR{power/control}="auto"}}
==Wireless power saving==
{{Accuracy|This method does not seem to work at the moment.}}
Enabling for a specific interface:
{{Note|This should be combined with [[udev#Network device|static naming]] of devices, the eth* names are not static.  In the below examples there are some assumptions about how your devices are named.  The first assumes that your wireless has the kernel name of "wifi0" and the second that any wireless interface will begin with "wlan".  Of course, with persistent naming included now in systemd, this is probably no longer the case.  "%k" in the second example is a variable for the kernel name for the matched device.  For example if it finds that the rule is applicable to wlan1, the "%k" variable will be replaced ith "wlan1".}}
{{hc|/etc/udev/rules.d/wlan0_power_save.rules|2=ACTION=="add", SUBSYSTEM=="net", KERNEL=="wifi0" RUN+="/usr/sbin/iw dev wifi0 set power_save on"}}
Enabling for all interfaces:
{{hc|/etc/udev/rules.d/wifi_power_save.rules|2=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:
{{hc|/etc/sysctl.d/dirty_writeback.conf|2=vm.dirty_writeback_centisecs = 1500}}
To do the same for journal commits with ext4 and some other filesystems, use {{ic|1=commit=15}} as a parameter in [[fstab]] or with the {{ic|rootflags}} [[kernel parameter]].
== Laptop Mode ==
{{hc|/etc/sysctl.d/laptop_mode.conf|2=vm.laptop_mode = 5}}
== 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.}}
{{hc|/etc/udev/rules.d/hd_power_save.rules|2=SUBSYSTEM=="scsi_host", KERNEL=="host*", ATTR{link_power_management_policy}="min_power"}}
== USB Autosuspend ==
To enable USB autosuspend after 2 seconds of inactivity:
{{hc|/etc/udev/rules.d/usb_power_save.rules|2=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 ==
{{accuracy|reason=Should be done with a udev rule.}}
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.
{{bc|<nowiki>function aa_power_settings ()
  sudo bash -c '
    for i in `find /sys/devices -name "bMaxPower"`;
        for ii in `find $i -type f`;
            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`;
                v=`cat $ff 2>/dev/null|tr -d "\n"`;
                [[ ${#v} -gt 0 ]] && echo -e " `basename $ff`=$v";
            done | sort -g;
    echo -e "\n\n\n+++ Kernel Modules\n";
    for m in `command lspci -k|sed -n "/in use:/s,^.*: ,,p"|sort -u`;
        echo "+ $m";
        systool -v -m $m 2> /dev/null | sed -n "/Parameters:/,/^$/p";
== See also ==
* [[CPU Frequency Scaling]]

Latest revision as of 12:30, 23 April 2015

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