Richard Hughes ([info]hughsient) wrote,
@ 2007-06-27 21:13:00
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powertop is getting it wrong...
The powertop utility from INTEL has been very interesting to use. Unfortunately, I'm quite pissed off.

"gnome-power-manager doesn't dim the backlight to save power it actually just changes the colour of the pixels on the screen"

Err no. It never has and never will. It actually dims the backlight on all the hardware I have tested it on.

Dimming to 30% when idle saves me about 1-3W of power on all three laptops I own. That's a X60 (ibm+intel), n100 (lenovo+nvidia) and a A10 (toshiba+old-intel).

For the X60, g-p-m calls HAL, which writes to the thinkpad_acpi controlled backlight class. This then writes a value into the embedded controller address space (or issues a CMOS command) which changes the hardware backlight brightness.

Really impressive graph by the way - but what crack are you smoking?

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quote removed?
[info]iquaid
2007-06-28 12:01 am UTC (link)
The quote doesn't seem to be anywhere on the linuxpowertop.org site; maybe the quote got removed? That was pretty fast. :)

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Re: quote removed?
[info]mr_z
2007-07-08 10:39 pm UTC (link)
If you mouse over the "backlight fix" triangle in the graph, you'll see this text:

The standard GNOME screen-brightness application (gnome-power-manager) does not actually change the brightness of the backlight on the T61, but only changes the color of the pixels on the screen. Using the xbacklight application to change the screen to the reference brightness does change the backlight power and saves almost 1 Watt.

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[info]ihatehandles
2007-07-07 03:06 pm UTC (link)
Maybe it changes the colors on CRTs since there isn't really a backlight to dim. Dimming the color on a CRT still does save power.

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seems true...
[info]nemik
2007-09-22 06:58 pm UTC (link)
they said it's for a T61. On my T61 g-p-m is first off hit/miss and brightness sometimes needs a HAL reset to work correctly.

Second, the xbacklight app reports the setting from ACPI. After adjusting brightness with g-p-m, it always reads 100 no matter what. It also doesn't adjust it correctly and the lowest setting is not at all like the lowest with xbacklight.

Since it does interface with HAL, this may be a HAL issue.

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