Comment 37 for bug 96240

Hey Bingo YOU rock! How about that? I'll just subscribe you so you see this reply though (you may want to unsubscribe yourself from this bug to avoid seeing replies).

As to your query, sync to vblank is there to stop tearing (at the cost of speed). Your monitor has a refresh rate and if things are not timed to be in sync with when a vertical blank takes place you can get tearing (imagine you have a black screen and you go to draw a white cube. If for whatever reason you can't draw the screen with the cube in less than the time it takes to refresh or you are unlucky then you will end up with half a cube at the bottom and a black screen at the top). See http://www.mythtv.org/wiki/index.php/Frame_display_timing for a better description.

(PS: if you want to see replies it is best to subscribe yourself to the bug you pose the question in)