Im running some throughput testing using OpenBSD as the router OS. Running the GENERIC.MP kernel im not seeing any system load despite the NIC's generating about 40 000 interrupts in vmstat.
Running the same test on a GENERIC kernel results in 80% system utilization. Checking with sysctl confirms that a pure interrupt based load from the NIC's doesn't update kern.cp_time. A userspace load like compiling the src tree however does show the expected behaviour and updates kern.cp_time. Im seeing this on both of my Dell machines. Dell 1750 with 4.0 MP kernel. Single core xeon. Runs MP to get APIC. Dell 1950 with -CURRENT as of yesterday. Dual core xeon.
