Growing frustration with Gnome Shell

[Alan Cox]

> Something about it also introduces a delay. If I run emacs in a plain
> old FVWM session with no 3D composting going on, it is perfectly
> functional.
> 
> If I run it under gnome-shell, I notice things like moving the cursor
> to extend the selection introduces a distinct delay that makes it
> very disconcerting to try and concentrate on what I'm editing
> rather than being constantly distracted by the random delays.
> 
> This is all on the same hardware with the same video driver, so
> the difference has to be gnome-shell.

The fancy effect setups render the images off screen for each window and
then the compositor sticks them together. Modern video hardware can blit
the bits of image around very fast, and the off screen rendering also
gets rid of much of the old annoying redraw effects X used to have all the
time but it does depend on the compositor running promptly and never
being blocked by other stuff as well as the compositor being smart about
how it does the frame compositing (eg by using vblank double buffering).

Phoronix looked at this:

http://www.phoronix.com/scan.php?page=article&item=linux_desktop_managers1

And Owen also has some further info on what is going on in the Gnome 3
case

http://blog.fishsoup.net/2011/06/13/benchmarking-compositor-performance/

There are some other IMHO slightly questionable choices in several
compositors, but at least people are benching and working on this stuff.

Alan