Difference between revisions of "Power saving"

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[[Category:Power management]]
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#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]].
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==Audio==
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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.
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{{Note|Toggling the audio card's power state can cause a popping sound or noticeable latency on some broken hardware.}}
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;Intel
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{{hc|/etc/modprobe.d/audio_power_save.conf|2=options snd_hda_intel power_save=1}}
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;ac97
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{{hc|/etc/modprobe.d/audio_power_save.conf|2=options snd_ac97_codec power_save=1}}
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==Active State Power Management==
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To verify that [[Wikipedia:Active State Power Management|ASPM]] is enabled:
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{{hc|$ cat /sys/module/pcie_aspm/parameters/policy|[default] performance powersave}}
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Either {{ic|[default]}} or {{ic|[powersave]}} means you do not need to force it on.
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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]].
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{{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.}}
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== Bluetooth ==
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{{expansion|reason=The device should likely be disabled with hciconfig first.}}
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[[Kernel_modules#Blacklisting|Blacklist]] the {{ic|hci_usb}} module if the driver is loaded automatically.
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==Disabling NMI watchdog==
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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.
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{{hc|/etc/sysctl.d/disable_watchdog.conf|2=kernel.nmi_watchdog = 0}}
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or add {{ic|nmi_watchdog}} as a [[kernel parameter]] to disable it completely from early boot.
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==Disabling Wake-on-LAN==
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[[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.
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Disabling for one interface:
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{{Note|This should be combined with [[udev#Network device|static naming]] of devices, the eth* names are not static.}}
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{{hc|/etc/udev/rules.d/disable_wol_eth0.rules|2=ACTION=="add", SUBSYSTEM=="net", KERNEL=="net0" RUN+="/usr/sbin/ethtool -s net0 wol d"}}
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Disabling for all interfaces:
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{{hc|/etc/udev/rules.d/disable_wol.rules|2=ACTION=="add", SUBSYSTEM=="net", KERNEL=="eth*" RUN+="/usr/sbin/ethtool -s %k wol d"}}
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== PCI Runtime Power Management ==
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{{hc|/etc/udev/rules.d/pci_pm.rules|2=ACTION=="add", SUBSYSTEM=="pci", ATTR{power/control}="auto"}}
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==Wireless power saving==
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Enabling for a specific interface:
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{{Note|This should be combined with [[udev#Network device|static naming]] of devices, the eth* names are not static.}}
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{{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"}}
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Enabling for all interfaces:
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{{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"}}
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== Writeback Time ==
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Increasing the VM dirty writeback time can help to aggregate I/O together - reducing disk writes, and decreasing power usage:
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{{hc|/etc/sysctl.d/dirty_writeback.conf|2=vm.dirty_writeback_centisecs = 1500}}
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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]].
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== Laptop Mode ==
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{{hc|/etc/sysctl.d/laptop_mode.conf|2=vm.laptop_mode = 5}}
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== SATA Active Link Powermanagement ==
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{{accuracy|reason=Should be done with a udev rule.}}
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{{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.}}
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echo min_power > /sys/class/scsi_host/host0/link_power_management_policy
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== USB Autosuspend ==
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{{accuracy|reason=Should be done with a udev rule.}}
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To enable USB autosuspend after 2 seconds of inactivity:
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for i in `find /sys/bus/usb/devices/*/power/control`; do echo auto > $i; done;
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for i in `find /sys/bus/usb/devices/*/power/autosuspend`; do echo '''2''' > $i; done;
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== Device Power Management ==
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{{accuracy|reason=Should be done with a udev rule.}}
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echo auto | tee /sys/bus/i2c/devices/*/power/control > /dev/null
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echo auto | tee /sys/bus/spi/devices/*/power/control > /dev/null
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== View Power Setings ==
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This function shows various power settings.  Note you either must be root or you must have sudo.
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{{bc|<nowiki>function aa_power_settings ()
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{
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  sudo bash -c '
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    for i in `find /sys/devices -name "bMaxPower"`;
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    do
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        for ii in `find $i -type f`;
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        do
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            bd=`dirname $ii`;
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            busnum=`cat $bd/busnum`;
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            devnum=`cat $bd/devnum`;
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            title=`lsusb -s $busnum:$devnum`;
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            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`;
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            do
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                v=`cat $ff 2>/dev/null|tr -d "\n"`;
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                [[ ${#v} -gt 0 ]] && echo -e " `basename $ff`=$v";
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                v=;
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            done | sort -g;
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        done;
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    done;
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    echo -e "\n\n\n+++ Kernel Modules\n";
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    for m in `command lspci -k|sed -n "/in use:/s,^.*: ,,p"|sort -u`;
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    do
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        echo "+ $m";
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        systool -v -m $m 2> /dev/null | sed -n "/Parameters:/,/^$/p";
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    done
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  ';
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}</nowiki>}}
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== See also ==
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* [[CPU Frequency Scaling]]
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Latest revision as of 12:30, 23 April 2015

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