Enabling KMS Radeon power management

06Dec10

Power management patches for Radeon devices were added to the mainline Linux kernel earlier this year (since 2.6.35???). These features can provide dynamic voltage and frequency scaling when running under KMS. This, of course only applies to the open source radeon driver and does not work on the fglrx driver from AMD/ATI. Currently by default the power management profile is set to ‘default’ which does not automatically switch power states or do any frequency scaling.

The following are two settings which can be used to set the power management state on radeon cards.

/sys/class/drm/card0/device/power_method
/sys/class/drm/card0/device/power_profile

The power_method option allows you to switch between the profile or dynpm method. The power_profile offers four options: default, auto, low, high.

The default settings are profile and default which uses the default clocks and does not change the power state.  dynpm is the most aggressive power management state however it only works on a single head configuration and may result in display flickering. I recommend setting the power_method to profile and the power_profile to auto. This will dynamically scale the GPU clocks down when the system is running on battery power.

On Ubuntu 10.10 the power management profile can be set by running the following commands.

sudo -i
echo auto > /sys/class/drm/card0/device/power_profile
exit

To set this configuration when the system boots add the second command to the /etc/rc.local file.

The current GPU clocks can be checked by running:

cat /sys/kernel/debug/dri/0/radeon_pm_info

Here are the results from my laptop using the auto profile.

When running on AC power:
default engine clock: 480000 kHz
current engine clock: 479250 kHz
default memory clock: 450000 kHz
current memory clock: 450000 kHz
PCIE lanes: 0

When running on battery:
default engine clock: 480000 kHz
current engine clock: 128250 kHz
default memory clock: 450000 kHz
current memory clock: 135000 kHz
PCIE lanes: 0

Reference


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