After looking recently at the impact on performance and power consumption of various Linux desktop environments running under Ubuntu 12.04 (Unity, Unity 2D, GNOME Shell, KDE, Xfce, LXDE, and Openbox), there were requests by many Phoronix readers to look at the impact of KDE on 3D gaming. KDE's KWin compositing window manager offers several options that can be easily changed that have a direct result on the Linux system's performance for full-screen OpenGL games.
To compliment the earlier Linux desktop testing, in this article is just running the KDE 4.8 desktop in Ubuntu 12.04 with various KWin window manager options. Multiple GPUs/drivers were tested.
Via the KDE system settings, the benchmarks were done when KWin was doing its compositing via OpenGL (the default), XRender compositing, and then when "Suspend desktop effects for fullscreen windows" was enabled. This option is not enabled by default since it can cause tearing/flickering for some on-screen overlays and other problems. The desktop effects during full-screen windows can also be disabled manually using "Alt + Shift + F12" or by a window-specific rule for the window that can be set by the application/game.
For this KDE effects testing an Intel Core i5 "Sandy Bridge" notebook was used as well as a workstation with ATI Radeon HD 4870 graphics on the open-source Radeon Gallium3D driver and the closed-source AMD Catalyst Linux driver. For the Radeon Gallium3D configuration, swap buffers wait was disabled during testing.
A variety of games was run automatically under the KDE desktop on Ubuntu 12.04 LTS x86_64 for these two systems via the Phoronix Test Suite.