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A Detailed Look At The ATI Linux Power Management

May 11, 2010, 17:32 (0 Talkback[s])
(Other stories by Michael Larabel)

"Last week we reported that the open-source ATI Linux driver had picked up improved power management in the form of dynamic power management and power management profiles that can be defined by the end-user. With the ATI Linux power management finally coming to fruition within the Linux kernel for its kernel mode-setting / DRM driver, we have decided to take a close look at how this power management support is working in the real world.

"Read last week's news post for more details on the work that has gone into the open-source ATI Linux power management support up to this point, as it's been a long-time in the making. To summarize, the patches posted by Alex Deucher of AMD last week clean-up the in-kernel ATI Radeon power management support for all ASICs and introduces these new power control options that are currently exposed to the end-user through a sysfs interface.

"The dynamic power management option introduced (via writing "dynpm" to the sysfs power_method node) will dynamically adjust the GPU's clock depending upon the graphics processor's load. This load determination is being done by looking at the number of pending GPU fences for the R500 (Radeon X1000) series and older. A fence on the graphics processor signals when the GPU has executed all instructions before it in the FIFO queue. In other words, the more fences that are pending, the more work the GPU still has to finish. For the Radeon HD 2000 (R600) series and newer there is a GUI idle IRQ interrupt support, but that is not working reliably for the R500 and older ASICs."

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