I have a Sony VAIO with Intel i7-3520M and NVIDIA Corporation GK107M [GeForce GT 640M LE]. I installed bumblebee and nvidia drivers. They work almost fine, but the system freezes like in a kernel panic once every day. I can play Dota 2 with primusrun on it with 20-30fps 1080p. But when I do something simple as expanding the KDE calendar widget from the bottom right corner, the system hangs a lot and windows borders get another border. The system freezes in not very intensive graphic tasks, for instance, ALT+TAB with KWin effects or pressing ALT+F2 for poping up the launcher. How can I solve this? Info: I use KDE. Couldn't paste de logs here, check at pastebin: http://pastebin.com/SBet8fRQ