A Detailed Look At The ATI Linux Power Management

While using the low power management profile provided about a six Watts savings for this dual-core Lenovo notebook, it does lead to quite a performance hit. The frame-rate in OpenArena had dropped from 42 frames per second under the default/high power states to just 22 frames per second when the power management support was maxed. This is the difference between making the game playable or not with its frame-rate being nearly halved. The dynamic power management option led to the same level of performance, which is showing that the time and calculations spent re-clocking the GPU are not causing a significant penalty.

Lastly, here are the results from World of Padman. The low power method led to the GPU losing well more than half of its performance dropping from 30 FPS to 12 FPS. The dynamic power management option continued to produce similar results to the high/default options.

It is great to see the ATI power management support finally maturing. It would be ideal to see much of this work land with the Linux 2.6.35 kernel, but as mentioned in the introduction this is not yet a perfect experience. While we did not run into any major problems during our testing over the weekend, some GPUs may misbehave when clocked too low or when the ATI Radeon GPU decides to re-clock itself when there is not a vertical screen blank. The dynamic power management support also does not work when an ATI graphics card is connected to multiple display heads. There is also greater power savings to come once this open-source driver supports dynamic voltage adjustments.

Unfortunately, as the proprietary ATI Catalyst Linux driver dropped support for the R500 ASICs -- thus the Mobility Radeon X1400 included -- we are unable to see how the power performance of the open-source driver stack now compares to the Catalyst driver that fully implements PowerPlay and other energy savings techniques.

In the end, using the low power profile is great if you are just using the Linux desktop and are not in need of a fast graphics processor. As the results show, there is quite a performance hit -- at least for the Mobility Radeon X1400 that can clock between 128MHz and 392MHz -- when forcing the GPU to always run at its lowest operational frequency. For all other cases, the dynamic power management support seems to be working out well as long as any bugs do not hit you.