$ glxgears
Running synchronized to the vertical refresh.  The framerate should be
approximately the same as the monitor refresh rate.
4 frames in 12.0 seconds =  0.332 FPS
2 frames in 12.0 seconds =  0.167 FPS
2 frames in 8.0 seconds =  0.250 FPS
2 frames in 12.0 seconds =  0.167 FPS