I have been experimenting with using the 14.104a SMP kernal and ver. 3.02 ACPI on 3 different Uni CPU machines in order to try to get /APIC to load the IRQ's high. The machines are:
1. AMD Mobile Athlon 64 3200+, VIA K8T800 chipset
2. AMD Athlon 64 3200+, NVidia3 chipset
3. Intel P4 3GHz, Intel 875P chipset
All will load the SMP kernal with and without the /SMP switch on ACPI. When I add the /APIC switch, they all hang after loading all the drivers, but (apparently) before running any RUN= statements. A hard reset is required. Even removing UniAud, GenMac, and USB drivers does not help.
There is one exception. Computer #3 (with P4) has hyperthreading. With hyperthreading turned ON, the computer boots with the /APIC switch. Turn hyperthreading off and it hangs again.
With hyperthreading on it seems every 3rd boot or so, the computer runs very slow because the CPU and IRQ load is very high, but the IRQ's are all shown as being >13.