Note: the following only applies to older version of SMP. Current versions no longer require this option.
Some motherboards provide inaccurate information about their 8254 timer INTerrupt connection to the I/O APIC, causing kernel lockup.
Add the following line to <SMP_SRC>/sys/i386/conf/<SMP_CONFIG_FILE>:
Then config, build, and install an APIC_IO kernel.