Comment 45 for bug 847001

Bug reappeared in 18.04.

Dell Precision M4800, running the standard Ubuntu Gnome shell desktop (on Xorg), Intel Graphics. No issues in 16.04 (or perhaps a tiny delay?), but unworkable in 18.04.

Both Fn-Up/Down and `echo value | sudo tee brightness` exhibit the delay (~2-3 seconds normally). Notable is that the brightness seems to change *immediately* after echoing into sysfs, so all the delay occurs in the return of the call back to the prompt.

In /sys/class/backlight I have only intel_backlight. No difference with or without Backlight option in xorg.conf, nor with the acpi_backlight=vendor kernel param.

Also notable: when performing the brightness change in a virtual terminal, it is *instantaneous*. The issue only occurs in the graphical VT running the desktop environment.