[How-To] Power saving with the Radeon driver

The open source driver for ATI cards has some power saving features. May not be that important for some desktop users, but for laptop users it's a must. The driver has two kinds of power saving schemes, one under UMS mode (older and more stable) and another under KMS mode. You can't use both methods at the same time. Most current distros have now defaulted to KMS, although none of them enable any power saving options in the drivers yet.  For this guide I will just focus on KMS, which is what most every current distro uses.
 

KMS

There are two methods.  One is the older profile based power switching.  This method is available for all cards that support power saving.  You will need the latest kernel available (minimum 2.6.35). To use it, simply execute the following command strings inside a terminal:

sudo -i
#to turn yourself into root

echo dynpm > /sys/class/drm/card0/device/power_method
## dynamic clock switching based on GPU load

echo profile > /sys/class/drm/card0/device/power_method
## profile based frequency switching; this is the default mode

If you select the profile method, you can then choose from several power profiles:

echo default > /sys/class/drm/card0/device/power_profile 
# uses default clocks/volts

echo low > /sys/class/drm/card0/device/power_profile 
## forces GPU to lowest available frequency; may cause some issues on certain laptops and displays, as this is the mode used when the display switches to dpms off mode

echo mid > /sys/class/drm/card0/device/power_profile 
## forces GPU  to be in the "mid" power state all the time; safer to use than "low" for regular desktop usage

echo high > /sys/class/drm/card0/device/power_profile
## forces GPU to highest available frequency

echo auto > /sys/class/drm/card-0/device/power_profile
## switches between high and mid power states depending on whether the system in on battery power or not

There is also DPM (Dynamic Power Management).  This is a newer (and better) method, though is only available for HD2K and newer cards and with kernels 3.11 and newer.  This method works more closely to how fglrx handles power management; clock switching should be automatic.  DPM is not enabled by default in the 3.11 kernels, where you have to add radeon.dpm=1 to your kernel parameters.  If you are using kernels 3.12 or newer, then DPM is enabled by default.

DPM can be further tweaked to your needs with the terminal.  First you need to learn that your card will have different power states and performance levels.  Each power state has three performance levels, which you can set manually.   Read the blog entry linked to at the end of this guide to learn more about this.

Usage is similar to the method above:

The default is the balanced power state and the auto performance level.  You can change them to you hearts desire.

There is also a nifty GUI called radeon-profile if you don't want to mess with the terminal.  Link is at the end of the guide.

Notes

1) DPM works for a lot of people, but for me it only kind of does.  My HD7850 still spends about 90% of the time in "3d" clocks and voltage.  I have to manually set it to low.  

2) There was an issue with APUs and the open source drivers where they would default to the low power state without being able to change the clocks. DPM supposedly fixes this issue and APUs now correctly re-clock to proper performance levels.

Links of interest:

agd5f's blog post on DPM

radeon-profile