I'm using TwinView and 2 LCD monitors with 1280x1024 resolution. Compiz is:
- fast if I disable TwinView,
- slooow if I enable TwinView,
- fast again if I enable TwinView and enable NoTwinViewXineramaInfo in xorg.conf, but then windows open between the screens which is nasty.
This last point indicates that it's not a problem with the driver or TwinView, but with enabling Xinerama, because this NoTwinViewXineramaInfo hack only disables Xinerama info and does nothing else.
Normally Compiz takes almost no CPU time with any operations. Slooow with TwinView and Xinerama means that it starts to take 50% upto 100% CPU time even with simple operations such as moving a window of a medium size (i.e. not fullscreen).
My system is Gentoo 64-bit, kernel 2.6.22, nvidia-drivers-100.14.11, xorg-7.2, compiz-0.5.2, xfce4-4.4.1.
I was encountering exactly the same problem with Beryl 0.1.2.
I can't reproduce this. Please re-open at bugs.opencompositing.org if you're still seeing this sort of slow-down. Sorry for the inconvenience.