patrick@linux:~> LIBGL_DEBUG=verbose glxgears
 1263 frames in 5.0 seconds = 252.600 FPS
 1320 frames in 5.0 seconds = 264.000 FPS
 1200 frames in 5.0 seconds = 240.000 FPS
 1320 frames in 5.0 seconds = 264.000 FPS
 X connection to :0.0 broken (explicit kill or server shutdown).
 patrick@linux:~>