https://bugs.freedesktop.org/show_bug.cgi?id=39202
--- Comment #22 from Michel Dänzer michel@daenzer.net 2011-08-16 02:34:28 PDT --- (In reply to comment #21)
[...] where should I put vblank_mode=0 to see the effect it does into kde?
Wherever kwin is started. E.g. you can try restarting it manually:
vblank_mode=0 kwin --replace