I have a Sony Vaio S13 laptop with a Nvidia 310M graphics card. Ever since I installed Ubuntu on it (11.10, now running 12.04) I have been having a recurring problem with the brightness controls. Besides the need to edit /etc/X11/xorg.conf and adding
EnableBrightnessControl=1, some times brightness controls are very laggy and unresposive (needs 2 or more key strokes to respond).
I've found a workaround that consists in generating a new xorg.conf file with
nvidia-xconfig, re-adding the brightness line and rebooting, however a few sessions later the problem is back again.
I still have not found when exactly does this happens and how to reproduce it, however it seems to have something to do with power management, as it often starts on the boot after changing from AC power to battery or vice-versa. On the other hand, it may be related to something that happens during boot or shutdown.
Does anyone has a similar problem and knows a fix?
EDIT: Found a nice workaround with Gnome 3 Extension Brightness Control. Unfortunately I can't set the Fn Keys to increase or decrease brightness, but setting a similar combination (e.g. Super+F2), there is absolutely no lag.