DragonFly bugs List (threaded) for 2007-04
Re: lenovo R60 SMP/APIC_IO woes
:Hmm. I though APIC_IO was needed for SMP to work... I've
:never been 100% sure about how the two
:are coupled though.
Most SMP systems ought to work without APIC_IO. Basically there are
two types of APICs. Each cpu has a LAPIC, and the motherboard chipset
has one or more IOAPICs. SMP requires the per-cpu LAPIC to be present
but doesn't require the IOAPICs.
When you compile a SMP kernel without APIC_IO it will compile in LAPIC
support but not IOAPIC support, and depends on the legacy 8259 (called
the 'PIC') to route interrupts, which is sometimes more compatible
with the BIOS.
There are lots of potential gotchas but usually a SMP box will work
in one or the other modes (IOAPIC or legacy PIC). If all else fails
you can turn on emergency interrupt polling in /boot/loader.conf or
with a sysctl. With emergency interrupt polling turned on only the
timer and IDE disk IRQs need to be properly routed, and they
kern.emergency_intr_enable (default 0 = off)
kern.emergency_intr_freq (default 10 = 10hz)