Difference between revisions of "Power saving"

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[[Category:Power management]]
#REDIRECT [[Power management]]
{{Related articles start}}
{{Related|Power management}}
{{Related|CPU frequency scaling}}
{{Related|Hybrid graphics}}
{{Related|Kernel modules}}
{{Related articles 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 [[Wikipedia:Intel Turbo Boost|dynamic overclocking]].
== Configuration ==
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.
{{Note|Most rules described below are also managed by tools like [[TLP]] and it is unwise to use multigoverning.}}
=== Audio ===
By default, audio power saving is turned off by most drivers.  It can be enabled by setting the {{ic|power_save}} parameter; a time (in seconds) to go into idle mode.  To idle the audio card after one second, create
{{hc|/etc/modprobe.d/audio_powersave.conf|2=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.}}
=== 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:
# set backlight level
SUBSYSTEM=="backlight", ACTION=="add", KERNEL=="acpi_video0", ATTR{brightness}="1"
See [[Backlight]] for more information.
=== Bluetooth ===
{{expansion|reason=The device should likely be disabled with hciconfig first.}}
To disable bluetooth completely, [[Kernel_modules#Blacklisting|blacklist]] the {{ic|btusb}} and {{ic|bluetooth}} modules.
To turn off bluetooth only temporarily, use {{Pkg|rfkill}}:
# rfkill block bluetooth
Or with udev rule:
# disable bluetooth
SUBSYSTEM=="rfkill", ATTR{type}=="bluetooth", ATTR{state}="0"
Or just [[enable]] the instantiated {{ic|rfkill-block@bluetooth.service}} provided by the {{Pkg|rfkill}} package.
=== Web camera ===
If you will not use integrated web camera then [[Kernel_modules#Blacklisting|blacklist]] the {{ic|uvcvideo}} module.
=== Kernel parameters ===
This section uses configs in {{ic|/etc/sysctl.d/}}, which is ''"a drop-in directory for kernel sysctl parameters."''  See [http://0pointer.de/blog/projects/the-new-configuration-files The New Configuration Files] and more specifically [http://0pointer.de/public/systemd-man/sysctl.d.html systemd's sysctl.d man page] for more information.
==== 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}} to the [[kernel parameter|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:
{{hc|/etc/sysctl.d/dirty.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 ====
See the [https://www.kernel.org/doc/Documentation/laptops/laptop-mode.txt kernel documentation] on the laptop mode 'knob.' ''"A sensible value for the knob is 5 seconds."''
{{hc|/etc/sysctl.d/laptop.conf|2=vm.laptop_mode = 5}}
=== Network interfaces ===
[[Wikipedia:Wake-on-LAN|Wake-on-LAN]] can be a useful feature, but if you are not making use of it then it is simply draining extra power waiting for a magic packet while in suspend. Disabling for all Ethernet interfaces:
{{hc|/etc/udev/rules.d/70-disable_wol.rules|2=ACTION=="add", SUBSYSTEM=="net", KERNEL=="eth*", RUN+="/usr/bin/ethtool -s %k wol d"}}
To enable powersaving on all wireless interfaces:
{{hc|/etc/udev/rules.d/70-wifi-powersave.rules|2=ACTION=="add", SUBSYSTEM=="net", KERNEL=="wlan*", RUN+="/usr/bin/iw dev %k set power_save on"}}
In these examples, {{ic|%k}} is a specifier for the kernel name of the matched device.  For example, if it finds that the rule is applicable to {{ic|wlan0}}, the {{ic|%k}} specifier will be replaced with {{ic|wlan0}}. To apply the rules to only a particular interface, just replace the pattern {{ic|eth*}} and specifier {{ic|%k}} with the desired interface name. For more information, see [http://www.reactivated.net/writing_udev_rules.html Writing udev rules].
In this case, the name of the configuration file is important. Due to the introduction of [[Network configuration#Device_names|persistent device names]] via {{ic|80-net-name-slot.rules}} in systemd v197, it is important that the network powersave rules are named lexicographically before {{ic|80-net-name-slot.rules}}, so that they are applied before the devices are named e.g. {{ic|enp2s0}}.
=== Bus power management ===
==== 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 is either unsupported or broken on your hardware, or has to be forced on with {{ic|1=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 does not work.
* On systems that do not support it forcing on ASPM can even increase power consumption.
==== PCI Runtime Power Management ====
{{hc|/etc/udev/rules.d/pci_pm.rules|2=ACTION=="add", SUBSYSTEM=="pci", ATTR{power/control}="auto"}}
==== Device power management ====
{{Accuracy|Mass enabling for nearly all devices has negative side effects (unwanted devices such as USB are included, worse performance of the udev rule since matching devices that enable power management by default is useless, harder troubleshooting, etc). Enabling per bus/class for the devices that need it should be recommended instead.}}
Enable power management for (almost) all devices, ''including USB'':
# Various subsystems runtime power management (by bus or class)
ACTION=="add", SUBSYSTEMS=="*", TEST=="power/control", ATTR{power/control}="auto"
# Various subsystems power saving (by module)
ACTION=="add", SUBSYSTEMS=="*", TEST=="parameters/power_save", ATTR{parameters/power_save}="1" </nowiki>}}
To list the various devices affected:
ls /sys/bus/*/devices/*/power/control
ls /sys/class/*/*/power/control
ls /sys/module/*/parameters/power_save
To enable power management for all systems ''except USB'', you could replace the first rule with individual rules for each subsystem instead (/sys/bus/''some_subsystem'', /sys/class/''some_subsystem''):
ACTION=="add", SUBSYSTEM=="some_subsystem", TEST=="power/control", ATTR{power/control}="auto"
==== USB autosuspend ====
The linux kernel can automatically suspend usb devices when they are not in use. This can sometimes save quite a bit of power, however some usb devies are not compatible with usb power saving and start to misbehave (very common for usb mice/keyboards). To mitigate the problem, you can pick one of the following udev rules based on your willingness to experience and solve problems that occur during everyday work. They are sorted in order of safety (safest, but least powersaving first):
The first option is to use a whitelist of devices, which '''you''' know are working:
SUBSYSTEM!="usb", GOTO="power_usb_rules_end"
ACTION!="add", GOTO="power_usb_rules_end"
TEST!="power/control", GOTO="power_usb_rules_end"
## Whitelist. Duplicate the following line with varying usbids
ATTR{idVendor}=="05c6", ATTR{idProduct}=="9205", ATTR{power/control}="auto"    # example: Qualcomm Gobi 2000
The second option is to blacklist devices that are not working with usb power management and enable it for all other devices:
SUBSYSTEM!="usb", GOTO="power_usb_rules_end"
ACTION!="add", GOTO="power_usb_rules_end"
TEST!="power/control", GOTO="power_usb_rules_end"
## Blacklist. Duplicate the following line with varying usbids
ATTR{idVendor}=="05c6", ATTR{idProduct}=="9205", GOTO="power_usb_rules_end"    # example: Qualcomm Gobi 2000
or to just enable usb power saving for all usb devices (not recommended):
ACTION=="add", SUBSYSTEM=="usb", TEST=="power/control", ATTR{power/control}="auto"
alternatively to the last udev rule you can add the following to ''/etc/modprobe.d/usb-autosuspend.conf''
options usbcore autosuspend=2
==== SATA Active Link Power Management ====
{{Note|This adds latency when accessing a drive that has been idle, so it is one of the few settings that may be worth toggling based on whether you are on AC power.}}
{{hc|/etc/udev/rules.d/hd_power_save.rules|2=ACTION=="add", SUBSYSTEM=="scsi_host", KERNEL=="host*", ATTR{link_power_management_policy}="min_power"}}
{{Warning|SATA Active Link Power Management can lead to data loss on some devices (e.g. Lenovo T440s [http://lkml.indiana.edu/hypermail/linux/kernel/1401.2/02171.html is known to suffer] this problem)}}
=== Hard disk drive ===
See [[hdparm#Power management configuration]] for details.
=== Mount options ===
You might want to use the {{ic|noatime}} option, see [[Fstab#atime options]] for more information.
=== CD/DVD spin down ===
{{Expansion|something similar without using udisks?}}
To allow the CD/DVD rom to spin down after a while using [[udisks]]:
# udisks --inhibit-polling /dev/sr0
== Tools and scripts ==
=== Packages ===
There are many scripts and tools which make use of the various settings described in the previous sections. These are notably:
* [[Powertop]] is a handy utility from Intel that displays which hardware/processes are using the most power on your system, and provides instructions on how to stop or remove power-wasting services. Its report functionality can also be used to identify the relevant parameters for the system. 
* [[TLP]]
* [[Powerdown]]
* {{AUR|powerconf}}
* {{AUR|ftw-git}}
* [[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.
{{Tip|Have a look at the [[:Category:Power management|power management category]] to get an overview on what power management options exist in Archlinux.}}
=== Using a script and an udev rule ===
Since systemd users can suspend and hibernate through {{ic|systemctl suspend}} or {{ic|systemctl hibernate}} and handle acpi events with {{ic|/etc/systemd/logind.conf}}, it might be interesting to remove [[pm-utils]] and [[acpid]]. There is just one thing systemd cannot do (as of systemd-204): power management depending on whether the system is running on AC or battery. To fill this gap, you can create a single [[udev]] rule that runs a script when the AC adapter is plugged and unplugged:
SUBSYSTEM=="power_supply", ATTR{online}=="0", RUN+="/path/to/your/script true"
SUBSYSTEM=="power_supply", ATTR{online}=="1", RUN+="/path/to/your/script false"
{{Note|You can use the same script that ''pm-powersave'' uses. You just have to make it executable and place it somewhere else (for example {{ic|/usr/local/bin/}}).}}
Examples of powersave scripts can be found here: [[powerdown]], {{AUR|powerconf}}, [https://github.com/Unia/powersave powersave].
The above udev rule should work as expected, but if your power settings are not updated after a suspend or hibernate cycle, you should add a script in {{ic|/usr/lib/systemd/system-sleep/}} with the following contents:
case $1 in
    pre) /path/to/your/script false ;;
if cat /sys/class/power_supply/AC0/online | grep 0 > /dev/null 2>&1
    /path/to/your/script true
    /path/to/your/script false
exit 0
Do not forget to make it executable!
{{Note|Be aware that AC0 may be different for your laptop, change it if that is the case.}}
Now you do not need pm-utils anymore. Depending on your configuration, it may be a dependency of some other package. If you wish to remove it anyway, run {{ic|pacman -Rdd pm-utils}}.
=== 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";
== See also ==
* http://forum.manjaro.org/index.php?topic=1166.0
* [https://wiki.ubuntu.com/Kernel/PowerManagement/PowerSavingTweaks Ubuntu Wiki's Power Saving Tweaks]

Latest revision as of 12:30, 23 April 2015

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