Radeon DRM: Dynamic Power Management Updates
Written by Michael Larabel in AMD on 5 July 2013 at 06:55 PM EDT. 80 Comments
The DRM pull request has yet to be submitted for the Linux 3.11 kernel and already there is another revision to the Radeon DRM kernel driver to be submitted. This latest Radeon DRM work provides additional dynamic power management fixes and some new sysfs features.

For open-source AMD Linux desktop users, the Linux 3.11 kernel is going to be spectacular as it finally brings Radeon dynamic power management support. While not yet enabled by default (the radeon.dpm=1 module parameter is needed for now), this finally provides dynamic re-clocking (like PowerPlay) so that GPUs can dynamically adjust their clock speeds and voltages based upon load. This is also good for APUs and newer GPUs so that the hardware can ramp up to its designated frequencies rather than being stuck to their boot frequencies.

Anyhow, on Friday AMD's Alex Deucher sent in another revised Radeon DRM driver. This revised code for the DRM subsystem in the Linux 3.11 kernel provides some dynamic power management fixes. The nine fixes include setting default clock speeds for AMD Radeon HD 7000 "Southern Islands" graphics processors when dynamic power management is enabled, support for 3D performance states on older GPUs, and adding in support for forcing performance levels.

Debugging entries were already added to an earlier revision for finding out the current power management state. With today's code, The new sysfs support allows forcing specific power levels within a power state. The forceable options allow for values of "auto" for all levels being enabled, "low" for forcing the lowest power level, and "high" for forcing the highest power level.

In terms of the 3D performance states for older GPUs, Deucher's commit message explains:
Certain older rv770 asics have both a performance and a 3D performance state rather than just multiple performance levels in the state power state. The current code would select the performance state rather than the 3D performance state when the "performance" profile was selected. This change switches to the "balanced" profile by default which ends up being the internal performance profile. When the user selects the "performance" profile, it selects the internal 3D performance state so the user can select the higher performance modes.

For most asics this changes nothing. For certain rv770 asics with static performance and 3D performance states, this allows you to select between then using by selecting the "balanced" and "performance" dpm profiles.

More details on these latesr Radeon DRM DPM fixes can be found via this mailing list message or browsing Radeon's drm-next-3.11.

Once Linux 3.11-rc1 is out, Radeon Dynamic Power Management benchmarks will begin at Phoronix.

About The Author
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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