Re: Poor Xinerama Performance
I've spent some time attempting to reproduce this problem. If I use two dis-similar GPUs, with Xinerama across 4 displays, such that I see the following warnings:
(WW) NVIDIA(2): The GPU driving screen 2 is incompatible with the rest of the
(WW) NVIDIA(2): GPUs composing the desktop. OpenGL rendering will be
(WW) NVIDIA(2): disabled on screen 2.
then I can reproduce the high CPU usage problem.
However, if I use two identical GPUs, with Xinerama across 4 displays, such that the above warnings are not present, then the problem is eliminated.
This points to the lack of OpenGL rendering support as the problem, as you're falling back to software, and thus, hitting the CPU for everything.
I'm afraid that there's no bug here. The solution to your problem is to use identical GPUs (or at least GPUs all from the same family) for all displays.