BSD 50% interrupt utilization in irq0/clock
This perticular problem was likely asperbated by the fact that OpenBSD's sysctl is anemic. FBSD "poll" sysctl would of likely solved this much earlier.
The problem was due to a poorly written BIOS, specifically it's configuration and implmentation of a console/remote access serial port. It was spinning like crazy and generating these interrupts, even if not connected etc...