DynamicPM vs. ClockGating in Radeon

[Melcar]

I got a question regarding the power saving options present in the radeon driver. OS being used is Ubuntu Karmic with the shipping radeon build (6.12.99), hardware is a laptop with an integrated 200M.
The manual descriptions for the options "DynamicPM" and "ClockGating" don't offer much explanation besides "reduces power usage". I would like to know exactly what they do and which one to use.
Right now I have both of them on (my xorg log confirms that they are being used) and I could immediately notice an increase in battery life, while performance stayed about the same as far as I can tell. What's the difference between the two? DynamicPM says it lowers power consumption while the system is idle which I guess simply means it downclocks the chip when there's no load on it; ClockGating isn't as descriptive but I assume it does the same. Are these two redundant options or do they do different things?

[bridgman]

They're totally different. Clock Gating enables internal logic inside the GPU that turns off the clocks to blocks which are not being used.

DynamicPM is an extension of ForceLowPowerMode (are you using that ?) which sets the engine clock very low when the the display is blanked by DPMS.

[Melcar]

I have both on at the moment. I guess having both on would be the best for aggressive power saving then (auto clock switching in normal use, low power when screen blanks out).

[bridgman]

You might want to enable ForceLowPowerMode as well. It reduces engine clocks and PCIE lane width at startup, which further reduces power at the expense of some performance.

[Melcar]

ForceLowPowerMode just keeps the chip at its lowest frequencies no, regardless of usage? I may try that, but right now I'm more than happy with the way things are.

[bridgman]

Yes, although it's "lower" rather than "lowest".

IIRC on radeon the ForceLowPowerMode option drops the clock speed to 50% of normal, while DynamicPM drops it to 25% but only when DPMS has shut down your display when the system is idle.

[Melcar]

Thanks. Understand things better now.

[TobiasTheViking]

Just wondering, since xorg.conf is being removed(i don't have one) how would one go about enabling those settings?

I mean, it isn't a problem for me to just make an xorg.conf, but i would rather do it the new way(if there is one yet that is).

[rohcQaH]

there is no generic new way. xorg.conf is not being removed, it's just possible to run X without one, using default settings. If you need non-default settings, create an xorg.conf.

(there are new ways for some of the more common options, e.g. modelines can be specified with randr instead of xorg.conf, but that doesn't apply to nonstandard driver options)

[TobiasTheViking]

Ah, ok. Thanks.

I thought it was being phased out.

Sincerely
Me