It's already been discussed at length within the Phoronix Forums following the results of Ubuntu's Unity/Compiz Gets Even Slower, Ubuntu Unity Proves Very Slow To KDE, GNOME, Xfce, LXDE, and 2D Also Bad For Ubuntu Unity Against KDE, GNOME, LXDE, Xfce, but there's some performance problems with the default Ubuntu desktop consisting of Unity and then Compiz as its compositing window manager.
In response to the test results and reader comments, Sam Spilsbury, a Canonical employee and leading Compiz developer, wrote:
I do not give ETAs on how long things will take. Needless to say, we are working on it, and some good ideas are being thrown around as to how to deal with it. That beingCompiz took a hit to make it work on ARM via supporting OpenGL ES, but chances are Compiz is only working on ARM if using one of the proprietary "binary blob" graphics drivers. If you're doing a clean Ubuntu 12.10 ARM desktop install, chances are it's a wreck as shown by the recent testing from an OMAP4460-powered PandaBoard ES.
1. Using glBlitBuffer instead of painting a texture backed framebuffer
2. Ensuring the contents of vertex buffers are more static (improves video)
3. Fullscreen window unredirection.
Thats not a promise that any of this will land *this cycle* per-se, but it is a note that we are aware there was a performance hit when we merged the work to make compiz work on arm platforms and we're actively dealing with it.
A Phoronix reader then asked a follow-up question concerning the release of Compiz 0.9.8.2. This minor Compiz update was released on 10 September and one of the key release highlights come down to "Gamers rejoice! CCSM Composite 'Unredirect Fullscreen Windows' now works more reliably, with a few bugs remaining. If you turn it on then fullscreen windows like games will get direct rendering access and won't be slowed by Compiz (or Unity) any more."
However, Spilsbury then responded in the forums that the unredirect full-screen window option basically isn't guaranteed to work right now with the Unity desktop due to some non-trivial reasons.
Un-redirected full-screen windows is one of the reasons why the KDE desktop does so much better than Unity and is an option easily exposed to the end-user since having a compositing window manager active when running a full-screen OpenGL game isn't as needed.
For the Unity/Compiz updates that come after the release of Ubuntu 12.10 next month, hopefully we will see them as stable release updates rather than waiting for Ubuntu 13.04 -- there's good chances of this seeing as Unity performance fixes have already landed during the Ubuntu 12.04 LTS cycle thus far.