Hi all,

I've been on a path of discovery lately regarding the state of play for 
ATI graphics cards. I started off using the ATI binary driver due to the 
high fan speed (resulting from high power usage) of the open source driver.

I decided to take a different approach today and stick with the open 
source 'radeon' driver. I managed to find that by default, the OSS 
driver keeps the card in a 'high power / performance' state.

This can be changed by using the sysfs entries exposed.

I found that using the following puts the card in low power mode:
	echo profile > /sys/class/drm/card0/device/power_method
	echo low > /sys/class/drm/card0/device/power_profile

Now, this is great to shut the fan up, and works on multi-head systems 
(more than one screen).

If you only use one screen, then you're in luck.
	echo dynpm > /sys/class/drm/card0/device/power_method

The "dynpm" method dynamically changes the clocks based on the number of 
pending fences, so performance is ramped up when running GPU  intensive 
apps, and ramped down when the GPU is idle. The reclocking is attemped 
during vertical blanking periods, but due to the timing of the 
reclocking functions, doesn't not always complete in the blanking 
period, which can lead to flicker in the display. Due to this, dynpm 
only works when a single head is active.

If you are like me and have multiple screens, you have the following 
options to get power_profile to:

"default" uses the default clocks and does not change the power state. 
This is the default behavior.

"auto" selects between "mid" and "high" power states based on the 
whether the system is on battery power or not. The "low" power state are 
selected when the monitors are in the dpms off state.

"low" forces the gpu to be in the low power state all the time. Note 
that "low" can cause display problems on some laptops; this is why auto 
does not use "low" when displays are active.

"mid" forces the gpu to be in the "mid" power state all the time. The 
"low" power state is selected when the monitors are in the dpms off state.

"high" forces the gpu to be in the "high" power state all the time. The 
"low" power state is selected when the monitors are in the dpms off state.

I've found that the 'low' setting seems to work fine in every day 
desktop tasks - and it certainly causes the fan to be much, much quieter 
than the default profile.

References:
* http://www.x.org/wiki/RadeonFeature

-- 
Steven Haigh

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Web: https://www.crc.id.au
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