Curious why vsync on, severely hinders performance?

[Kevin Kofler]

Victor B. Gonzalez wrote:
> I got the Nvidia binary 304.32 on KDE 4.9.00 on Fedora 17. KDE desktop
> effects run pretty flawless at 100+ FPS no matter what I do **but** the
> second I enable vsync on in desktop effect settings, FPS can drop to a
> choppy 30FPS. Why does this happen?
> 
> Not a solid 30 FPS but a choppy 30 FPS.

Limiting the framerate to ~30 FPS (i.e. what your screen can actually 
display) is exactly what vsync is for. Now why it's choppy, I don't know. It 
might be that the effects are not syncing with vsync, so the FPS varies 
depending on when vsync hits compared to what the rendering thread is doing, 
or it might just simply be a driver bug (proprietary drivers are always very 
buggy, try Nouveau!). (It could be a combination, like the driver failing to 
tell clients such as KWin that vsync is in use, which would of course be a 
driver bug.)

        Kevin Kofler