CPU governors and power supply status

Update: As announced, this script collection has been incorporated into my PPA as a package. Check it out here.

As promised, here's an article on CPU governors. As You might know by now, I use Ubuntu on my laptop. Unfortunately, it was kind of useless (until now) if I didn't plug in the power supply, since the battery was drained in less than an our of work (using nothing more than a text editor, kile). The problem source: The system doesn't change the cpu governor when the power cord is plugged out. Thus, the ondemand governor is used instead of the powersave one.
Luckily, there's an easy way to cope with this. The ACPI daemon acpid can be taught to execute arbitrary code upon any ACPI event. That means You can use it to automatically change the CPU governor depending on Your power supply status. Here's how it works:

1. Create a script to change the CPU governor. You can use mine, too:
   

   Code:

   #! /bin/bash # Note: AC connection is in: # /sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0003:00/power_supply/AC/online # 0 is disconnected, 1 is connected # If no arguments are passed, print governors if [ -z "$1" ] then    for MYCPU in /sys/devices/system/cpu/cpu[0-9]*    do :       echo "$(basename $MYCPU): $(cat ${MYCPU}/cpufreq/scaling_governor)"    done    echo "Available (on cpu0): $(cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors)"    exit 0 fi # Bring governor in control if [ "$UID" -ne "0" ] then    echo "Error: Must be run as root!"    exit 1 fi echo -n "Handling over control to $1 governor... " if [ "$1" == "conservative" -o "$1" == "powersave" -o "$1" == "performance" -o "$1" == "ondemand" ] then    for MYCPU in /sys/devices/system/cpu/cpu[0-9]*    do :       echo "$1" > ${MYCPU}/cpufreq/scaling_governor    done # userspace governor needs speed argument elif [ "$1" == "userspace" ] then    if [ "$2" -gt "0" ]    then       for MYCPU in /sys/devices/system/cpu/cpu[0-9]*       do :          echo "$1" > ${MYCPU}/cpufreq/scaling_governor          echo "$(expr $2 \* 1000)" > ${MYCPU}/cpufreq/scaling_setspeed       done    else       echo "userspace governor needs speed argument > 0!"    fi else    echo "Unknown governor: '$1'"    exit 1 fi echo "done"

   Make the script executable and place it somewhere, e.g. in /usr/local/bin. You can also use the script manually from the command line, e.g. with sudo cpufreq performance if You feel like You need everything Your computer got.
2. Create a script for the acpid and place it in /etc/acpi (the script must be executable). Mine is called powersave.sh and looks like this:
   

   Code:
   #! /bin/bash # Called by /etc/acpi/events/powersave # Calls cpufreq script to set cpu governor # Author: Frederik Möllers if [ "$4" -eq 0 ] then    /usr/local/bin/cpufreq powersave else    /usr/local/bin/cpufreq ondemand fi

3. Create a rule for the acpid and place it in /etc/acpi/events. Mine is called powersave and looks like this:
   

   Code:
   # /etc/acpi/events/powersave # Calls /etc/acpi/powersave to set cpu governor when ac adapter status changes # Author: Frederik Möllers event=ac_adapter action=/etc/acpi/powersave.sh %e

4. Make acpid reload its configuration (as root):
   

   Code:
   $ reload acpid

5. You might think You're done now, but actually You've only finished half of the job yet. When the system boots up, there will be no ACPI event telling acpid the status of Your power supply. Thus, if You boot with the power cord plugged out, Your system will still use the ondemand governor. To deal with that, You can create an upstart script which sets the CPU governor depending on the status of the power supply. Create a file /etc/init/cpufreq.conf (or with any other filename, but keep the .conf extension!) and fill it with something like the following.
   

   Code:

   # cpufreq # # Sets CPU governor to ondemand if AC is plugged in and powersave if not # Default is performance which is kind of overkill. description "CPU frequency scaling" author "Frederik Möllers" start on (virtual-filesystems and local-filesystems) script    if [ "$(cat /sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0003:00/power_supply/AC/online)" -eq 0 ]    then       sudo /usr/local/bin/cpufreq powersave    else       sudo /usr/local/bin/cpufreq ondemand    fi end script

   WARNING: Depending on Your system, the path (/sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0003:00/) on the /sys filesystem where the status of Your power supply can be found, may differ from the one I use. It shouldn't be miles away, but especially the number following ACPI may be another one on other laptop. You might need to search for the power_supply directory manually and change the path.
6. You're almost done! Since the default CPU governor is performance which, as I said in my script, is kind of overkill, Ubuntu ships with an init-script to set the governor to ondemand upon startup. This, however, collides with the upstart script You just created, so You need to disable that init-script (as root):
   

   Code:
   $ update-rc.d ondemand disable

   This will safely disable the ondemand script but will still offer You the chance to turn it back on if You ever want to revert the changes You made.

That's it! You're done!