Comment 9 for bug 987304

Hi Daniel,

I bisected the source code of Unity a little and i think i've found at least one revision which is causing the slowdown:

rev. 2226:

* Fix for bug #839480
* Fix rendering of the Dash, Launcher and Panel when "NO_BLUR" is selected in CCSM
* Added support to get a none blurred region of the display from BackgroundEffectHelper. Fixes: https://bugs.launchpad.net/bugs/839480, https://bugs.launchpad.net/bugs/941066. Approved by Gord Allott, Brandon Schaefer, Jason Smith.

When using Unity up to rev. 2225 moving windows around on the desktop and scrolling e.g. in Firefox is smooth and fast. Using rev. 2226 moving windows gets jerky and scrolling is slow. The latency of the whole desktop is much better with rev. 2225.

Benchmark with OpenArena (Running in a window):

Unity v5.12 -> 840 frames 41.6 seconds 20.2 fps 13.0/49.5/129.0/12.5 ms
rev. 2226 -> 840 frames 41.6 seconds 20.2 fps 20.0/49.5/117.0/11.1 ms
rev. 2225 -> 840 frames 36.6 seconds 22.9 fps 15.0/43.6/103.0/12.3 ms
Compiz -> 840 frames 29.8 seconds 28.2 fps 4.0/35.5/441.0/15.5 ms
IceWM -> 840 frames 25.0 seconds 33.6 fps 7.0/29.8/76.0/8.0 ms

The difference between rev. 2225 and 2226 is not that high but the desktop does not feel sluggish up to rev. 2225. After rev. 2226 the whole desktop feels like Unity 4.x before your FBO-fix with introduced. But as you can see Unity has a huge impact on the 3D-performance because when running Compiz without the Unity-Plugin the framerate of OpenArena is much higher.