You need to have read/write permissions to /dev/dri/cardX to benefit from 3D hardware acceleration in Xorg X Server. On a Gentoo linux machine, this file has the following permissions set by default :
ls -l /dev/dri/card0
crw-rw---- 1 root video 226, 0 2009-10-14 16:12 /dev/dri/card0
which means that a user has to be in the video group to have access to hardware 3D acceleration.
If you need help to diagnose 3D acceleration problems, you can run :
$ glxinfo | grep render
direct rendering: Yes
OpenGL renderer string: Mesa DRI R300 20060815 x86/MMX/SSE2 TCL
If you get either direct rendering is No, or OpenGL renderer string is “Software Rasterizer”, then you don’t have 3D acceleration.
You can further diagnose the problem by running : LIBGL_DEBUG=verbose glxinfo, which will hopefully provide more details on the problem.
And of course glxgears will give you a baseline for the FPS (frames per seconde), to check for any improvement before and after you changed any parameter.
On Gentoo, the glxinfo is part of the x11-apps/mesa-progs package.