Unity, which uses Compiz and Nux for drawing, recently had a regression with full screen gaming speeds (LP: #1024304). While the performance of Compiz itself was improved significantly in Ubuntu 12.10, the big changes like full OpenGL ES support brought in some regressions at least from benchmarking point of view. Unity/Compiz has had a small performance impact also in Ubuntu 12.04 LTS depending on what it's being compared to. Any compositing method will necessarily bring some performance hit, but there's another option...
Many people know already about enabling the setting "Unredirect Fullscreen Windows" in Compiz's Composite plugin, but having to enable it manually meant that most people didn't get to use it. The feature detects when an application is running full screen, and simply takes compositing out of the equation, improving performance. Getting the feature work fluently has required fixes in both Compiz and drivers, which is why it hasn't been enabled by default before (LP: #1063690).
But things are progressing now. The Unity team's SRU PPA now has a test build of the new Compiz 0.9.8.6 for Ubuntu 12.10, which enables this feature by default:
Since Phoronix is a frequent reporter on Linux gaming performance, I (very) quickly run phoronix-test-suite's Open Arena test on my Sandy Bridge machine with the stock Ubuntu 12.10 (quantal) Compiz and with Compiz upgraded from the PPA: 18% increase in fps! (test1_1 has older compiz, test1_2 the newer, no settings touched)
The idea is to get the new Compiz into quantal-proposed after the previous snapshot release 1:0.9.8.4+bzr3412-0ubuntu0.1 gets its bug fixes properly verified via the Stable Release Updates process. Note that also this previous snapshot contains all the needed fixes for unredirecting fullscreen windows, the final tagged 0.9.8.6 version just switches the default to be enabled.
For Ubuntu 12.04 LTS (precise) there will be two steps. First of all, Daniel van Vugt has just backported the required Compiz fixes to the 0.9.7 branch of Compiz that the 12.04 LTS uses and tagged the 0.9.7.10 release. Also in the case of precise, there is an earlier snapshot release in the SRU system, but that one does not yet include the needed backports even though it includes many other fixes. The 0.9.7.10 will be available in the same SRU PPA soon. Secondly, once the fixes are in but the feature is not yet enabled by default, the X.org driver team will need to look at additional fixes for the drivers before enabling the Unredirect Fullscreen Windows by default. But after that, Ubuntu 12.04 LTS should also see a Compiz release with this feature turned on by default.