For some time the default clock rate on RedHat machines (and probably others) have been 1000HZ, this is great to keep your mouse moving smooth while something big is happening in the background, but not so great for hosting 10 virtual machines on one poor physical machine as it will have to try and satisfy 10000 ticks per second.
I’ve been using a guest kernel repository by one of the VMWare users that rebuilds the std CentOS/RedHat kernels with HZ=100 and it’s been great, chopped massive amounts off my CPU usage on the host.
Now with RedHat 5.1 this is not needed anymore see this post for a bit of a graph on the impact and the background. The short of it is, simply append divider=10 to your guest kernel boot parameters and enjoy a much happier host. I found that time keeping also becomes more predictable in the guest.
