In Blackwood are with my Hardware no frames buffered. Therefore i have in Blackwood nonsmooth graphics. I suggest, that the nunber of buffered frames are no longer "maximum buffered frames", rather the number of buffered frames should be a fixed value, that when setup buffered frames to 2 always 2 frames buffered and no longer sometimes no frame buffered.

You are aware that having 2 buffered frames at all times is exactly the same as having zero but with a little delay, right?

Buffering 2 frames serves the purpose to use one if the one is rendering finishes too late. If it is not enough, then is your computer fault, LFS can't pull out frames out of the blue.