EARLY_AP_STARTUP hangs during boot

I tried out EARLY_AP_STARTUP, but the kernel hangs and I can't
break into DDB.

I did a verbose boot and the last lines I see are related to routing
MSI-X to various local APIC vectors.  I copied the last few lines and
they look like this:

msi: routing MSI-X IRQ 256 to local APIC 2 vector 48
msi: routing MSI-X IRQ 257 to local APIC 3 vector 48
msi: routing MSI-X IRQ 258 to local APIC 4 vector 48
msi: routing MSI-X IRQ 256 to local APIC 0 vector 49

I tried disabling msi and msix in /boot/loader.conf, but the settings
were ignored (probabaly too early).

I'm running on a AMD Phenom(tm) II X6 1090T Processor.

So, maybe this option only really works correctly on Intel CPUs?

-- 
Gary Jennejohn