virtualbox.org

I've noticed a strange CPU usage form vboxheadless running on our MacPro 4x2.66 with OS X 10.5 Server as host. What's the strange? With only one VirtualBox running, the VBoxHeadless process has about 20% of CPU usage (20% from a single core) with guest OS (Win2003) in idle; it's no a little percentage, but the strange comes if I lunch a second VirtualBox: both go to 6-7% of CPU with idle guest. So I have less CPU usage with two running VirtualBox than with only one.
Guest OS (both Win2003) in idle are between 1 and 3% of virtual CPU, as shown in task manager. Both have no antivirus ore other strange process in act.
If I stop one of two VirtualBox, the other goes up agin to 20%.
Can someone try if he has a similar CPU usage?

I'm seeing about 14% CPU utilization on my Mac Pro. It's an eight-core Xeon machine (not the new Nehalem) with 8 GB RAM running Vista x64 as a guest with 2 GB RAM. It's also running VirusScan Enterprise.

I don't remember exactly where I saw it, but I remember reading an article about modifying Windows' idle process to prevent it from churning up host processing power. If I come across that again, I'll try it out and post the results here.