How Unity, Compiz, GNOME Shell & KWin Affect Performance
Phoronix: How Unity, Compiz, GNOME Shell & KWin Affect Performance
Those that follow my Twitter feed know that over the weekend I began running some benchmarks of the various open-source and closed-source graphics drivers. But it was not like the usual Phoronix benchmarks simply comparing the driver performance. Instead it was to see how each driver performed under the various desktops / window managers now being used by modern Linux installations. In this article are the first results of this testing of Unity with Compiz, the classic GNOME desktop with Metacity, the classic GNOME desktop with Compiz, the GNOME Shell with Mutter, and the KDE desktop with KWin. These configurations were tested with both the open and closed-source NVIDIA and ATI/AMD Linux drivers.
Oops, it seems an important factor was forgotten...
You didn't mention, in the test, the use of the Compiz or KWin options that disable compositing for fullscreen apps, thus games !
* By default, KWin turns off compositing for fullscreen apps and should be as fast as Metacity (don't know why it turns out to be faster ?!). This option is great but makes the screen flicker a little when switching from windowed to fullscreen mode. In the future, there will be an API, apparently, so that apps can tell if they are more demanding or not, and if compositing should be switched off or not. (way to go, IMHO !)
* By default, Compiz doesn't and you have to install "ccsm" and tick "undedirect fullscreen apps" and you want to play games with the most FPS.
I'm pretty sure KWin would not be faster than Compiz, if that was taken into account. (well, there will be MUCH performance improvement in KDE 4.7, too)