Difference between revisions of "Power saving"

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[[Category:Power management]]
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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]].
 +
 
==Audio==
 
==Audio==
  
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{{hc|/etc/modprobe.d/audio_power_save.conf|2=options snd_ac97_codec 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|In some cases forcing on ASPM can even increase power consumption.}}
 +
 +
== 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
 +
 +
== 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/sbin/ethtool -s %k wol d"}}
 +
 +
You can use multiple names in the matches; for example, {{ic|1=KERNEL=="lan0|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==
 +
 +
Enabling for a specific interface:
 +
 +
{{Note|This should be combined with [[udev#Network device|static naming]] of devices, the eth* names are not static.}}
 +
 +
{{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 Powermanagement ==
 +
{{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"`;
 +
    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";
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            for ff in `find $bd/power -type f ! -empty 2>/dev/null`;
 +
            do
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                v=`cat $ff 2>/dev/null|tr -d "\n"`;
 +
                [[ ${#v} -gt 0 ]] && echo -e " `basename $ff`=$v";
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                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
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        echo "+ $m";
 +
        systool -v -m $m 2> /dev/null | sed -n "/Parameters:/,/^$/p";
 +
    done
 +
  ';
 +
}</nowiki>}}
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 +
== See also ==
 +
 +
* [[CPU Frequency Scaling]]

Revision as of 15:11, 25 November 2012

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.

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.

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

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: In some cases forcing on ASPM can even increase power consumption.

Bluetooth

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

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*"

Note: This should be combined with static naming of devices, the 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:

Note: This should be combined with static naming of devices, the eth* names are not static.
/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

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.
/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

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

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
  ';
}

See also

Retrieved from "https://wiki.archlinux.org/index.php?title=Power_saving&oldid=236762"