assigning interrupts

[Jeremy Chadwick]

On Thu, Nov 13, 2008 at 04:40:03PM +0100, Joerg Sonnenberger wrote:
> On Thu, Nov 13, 2008 at 02:40:54AM -0800, Jeremy Chadwick wrote:
> > Otherwise, consider purchasing a motherboard that has an APIC (this is
> > not a typo) increasing the IRQ count to 256.
> 
> This is wrong. The first IO-APIC gives you 8 additional interrupts to
> the 16 ISA interrupt lines. Every additional IO-APIC gives you 24 more.
> Most modern chipsets have one IO-APIC, at least for non-embedded
> systems. It doesn't mean you don't get interrupt sharing though.

I think the problem is that I was thinking of local APICs, which provide
a few hundred (I don't remember the exact number) IRQs to an I/O APIC.

For what it's worth, the devices he listed are exclusively on the PCI
bus.

Regarding "it means you can still get interrupt sharing", I'd like to
hear more about why/how that's possible with a system sporting at least
one I/O APIC.

-- 
| Jeremy Chadwick                                jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |