Saving 33% or 3 Watts of Power with your Netbook (here a Poulsbo system)

I've tried around a lot to see how much more power I can save on my system. An easy step with lots of success was to configure the laptop tools to run automatically. Check /etc/defaults/acpi-support and looks for LAPTOP_MODE, set it to true. Then you have to go to /etc/laptop-mode/ and configure first laptop-mode.conf and then the additional settings in the conf.d subdirectory. This could already save me at least 1 watt of power with very, very little hassle.

Poulsbo
I've tried around a lot with my X system, because it can draw a lot or little power depending on its settings. E.g. if you reduce the backlight you can save at least 2 watt power. Unfortunately the backlight controls on my system don't work - I'm happy I've managed to get the driver to run at all. (Check my special article on the MSI Wind U110 for more on that.) Hence at least for now I need to set my backlight to the level I want before booting Linux.

But I did find out that disabling vsync saves quite a substantial amount of power, I think about 0.5 watt. Most of the savings come from the cpu staying in idle longer on average then (about 22 msecs instead of about 4-8 ms). The catch is that with that setting enables, xvideo and vaapi no longer work after standby. Browsing is still fine, but probably no youtube, either. The whole system hangs when an application tries to use xv. So I had to disable the setting again - which actually was the step to put my netbook in a lower power mode than the carefully customized windows installation can manage, too bad.

If I pass it or any options (except debug) to the psb module during load, or load it myself during boot, X or suspend won't work at all or properly or properly after standby.

In the xorg.conf I have the standard settings for psb:

Option "AccelMethod" "EXA"
Option "DRI" "on"
Option "MigrationHeuristic" "greedy"
Option "IgnoreACPI" "yes"

Ralink Wifi
Another big one was the wifi adapter. Disabling it saves about 1.5-2 watts power, but of course I wanted to be able to have it running and save energy as well. I installed the newest driver from ralink's homepage. The important step was to go into the os/linux/ directory and edit the config.mk file to enable HAS_NATIVE_WPA_SUPPLICANT_SUPPORT=y, otherwise NetworkManager would no longer work with it. Then I studied the documentation and found the command "iwpriv ra0 set PSMode=Fast_PSP" put my card into a low power mode which still keeps a good and rather fast connection - better than in Windows, there this powersaving mode does not exist and the MAX_PSP is unusable.

Last Hint
A last additional hint is to kill knotify4.

Conclusion
In the end my system runs with 5.7 watts in a full KDE 4.3.2 X session. With mplayer and VAAPI I can now watch movies for at least 8 hours. A great demonstration of how far Linux has already come in saving power.

The only thing missing now is a working backlight control and a working XVideo without vsync would be great. Ok, an SSD would be great, too. So let me know if you have one you no longer need! ;) Or if you know how to fix the backlight control on a poulsbo system.

Maybe I should try to compile the IEGD driver for my system.

Update
I've manged to get it all running, including no_vsync, and videoacceleration before and after suspend. The trick is to do a double console switch after resume. Then VAAPI still works even after the suspend and resume - at least with xserver-xorg-video-psb version 0.36.0-0ubuntu1ppa9.10+1.

Update2
I've managed to get the backlight working roughly as well! All I needed to do was to load msi-laptop with the parameter force=1. The problem is that there is so far very little scaling, I can only set brightness to 0 (very dark) or 1-8 (all "very bright").

Update3
Check out this article with more general advice including how ensure your battery lives long and prospers. Backlight is fixed by now, I've written a patch for the psb driver (in testing at the ppa right now). With recently kernels, the power usage dropped down to 4.8 Watts without wifi! This means it lasts much longer in Linux than in Windows now.