Compiz using 40% CPU on Ubuntu 13.10

The high CPU use could be due to fallback to the software renderer. You can verify whether or not you're using the software renderer by executing the following command on the command-line:

/usr/lib/nux/unity_support_test -p

If the result is as follows:

Not software rendered:    no

That indicates that the software renderer is being used (nice use of a double negative there). In that case, installing the latest version of the Intel graphics drivers, as recommended in another comment, should help. However, as of November 28, Ubuntu 13.10 is not yet supported by the Installer. It appears to be one of those "any time now" situations.

In the meantime, I was able to fix the problem on my system (ThinkPad T420S) by installing the drivers via the oibaf ppa which supports Ubuntu 13.10. unity_support_test now verifies that software rendering is disabled. Hope this helps and let us know if you managed to fix the issue, as well.