First, if you are running PB-related tools, try with them turned off. As with BC2, tools like pbbans cause many of the performance problems that we see.
Second, if you're running an admin tool that is sending a lot of commands to the server, try turning it off or easing its commands up a bit. As with BC2, sending a lot of commands to the server can slow it down.
If neither of these help, and you see high CPU usage on the "Health" page of your control panel, please contact us, and we can try moving you to a different machine.
BF3 is mostly single-threaded, but can be configured to partially use more processors. On slower platforms (such as VDSes with lower-clocked cores), adjusting this may be beneficial in allowing larger servers to be run; this option is on the "Managed panel" for managed customers.
The game itself also seems to have some problems with performance, especially on certain maps, regardless of the hardware platform. DICE is looking into these and says that rubber-banding should be reduced in the next server version.