Desktop Effects Power Consumption
I recently installed the KDE4 version of Kubuntu on my laptop using the Wubi installer and was able to start using KWin's desktop effects on my laptop for the first time. I wasn't able to do so in the past because I didn't have a native install and VMware Player doesn't support hardware acceleration.
The Wubi installer was a great solution because it allowed me to install Kubuntu without disrupting my existing OS and also allows access to any existing files on the local hard drive.
After installing KDE4.1 beta 1 I started to get curious about battery life. I had heard that Vista's 3D desktop decreased battery life and wondered if KWin did the same.
My tools for testing power draw were Powertop and an applet called KPowersave. Powertop reports a power estimate and processor states and what processes cause the most wake events. KPowersave reports the number of milliwatts being drawn from the battery and provides a reasonable comparison point. It also allow you to set power management profiles and monitor battery status and real time CPU frequency.
Quick tip: Alt+Shft+F12 toggles desktop effects on and off.
To my surprise the reported difference was relatively small at only ~400mW while idle, or during light use like typing or reading a web page. Even playing a video had a similar result. I did see higher utilization while using the Cover Switch Alt+Tab effect, but even then it was only ~1W.
Because the difference was so low I decided to test my LCD backlight as a control experiment. This time the results were much closer to what I expected. There was a 4-4.5W difference between to most and least bright settings.
My original curiousity was due to wanting to keep my battery life as long as possible. With KWin desktop effects being such a minor contributor I definitely plan to leave it enabled unless I know I'll need every minute of available time.
Despite some critisms of KDE4 focusing too much on appearance or being "bloatware" my experience has been a significant performance improvement over previous versions and over Windows XP on the same machine. The new KWin makes working and switching between apps a completely smooth experience. And in case you think a lot of 3D compute performance is needed, it's not. I'm running on Intel 915 integrated graphics that's a few generations old.