Bug#673424: bbswitch packaging

[Ralf Jung <post@ralfj.de>]

Hi,

> I suppose a better way of explaining why watching /proc/acpi/bbswitch
> isn't reliable is by referencing the differences between how the
> virtualgl and primus backends work. Virtualgl will always cause the
> secondary X server to be spawned (everything is rendered on the
> secondary X server before being displayed on the primary X server),
> whereas primus will only offload glx calls to bumblebee, thus the
> secondary X server will only start up when you run some sort of opengl
> application with primus. That means that "optirun bash" or "optirun
> xterm" will invariably turn on the secondary X server and the nvidia
> gpu, whereas "primusrun bash" or "primusrun xterm" (or some other
> application that doesn't use any glx calls) will not.
However, if primusrun is invoked via optirun, then the second Xserver is
spawned immediately - optirun itself does that before launching primusrun.
In this scenario, primusrun has the advantage of keeping the second
Xserver "alive" even if the program forks away, since primus is injected
in each sub-process which is launched, while optirun+virtualgl monitor
only the initially executed process.

Kind regards,
Ralf