PowerTune: Taming Cayman
AMD introduced a feature called PowerTune with its Cayman-based cards. Simply put, you can think of PowerTune as a power cap for graphics cards. Can we use it to more granularly control power consumption? If the answer is yes, it would be pretty handy for users who do not have voltage adjustments available on their graphics cards.
We're going to test the Radeon HD 6970 at its default settings in our effort to gauge the usefulness of PowerTune. That means no voltage adjustments and no core or memory clock changes. The only variable we're changing is the PowerTune slider in AMD’s Catalyst Control Center, setting it to '-20'. For reference, we're also including results with the same clocks and the PowerTune slider set to 0 (its default setting). We're also including results from running the Radeon HD 6970 at 500/1030 MHz and 0.85 V.
Judging by the power consumption numbers, there doesn't seem to be any difference between the settings. The most likely explanation is that PowerTune simply isn't kicking in. If an application does not push the GPU to the point where PowerTune is needed to help scale back thermal load, then the card continues to operate without constraint.
In Medal of Honor, which is more GPU-intensive, PowerTune does kick in. At full clocks, setting PowerTune to -20 offers some savings, but the savings are smaller than running at UVD clocks. You incur less of a performance hit, and minimum frame rates are similar. At UVD clocks, PowerTune doesn't seem to offer any additional savings, probably because the card doesn’t come anywhere near approaching its thermal ceiling at these lower frequencies.
It's clear that PowerTune effectively changes operating frequencies dynamically when it considers power usage in excess of its limits.
Using PowerTune to cap power consumption does work, though it’s limited to games and applications with very high GPU utilization. In contrast, the UVD trick works regardless of the software you use. It also offers higher power consumption savings. To its credit, PowerTune is more convenient, since you can save the settings as a switchable profile in Catalyst Control Center.