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Date: Thu, 13 Nov 2008 18:34:52 +0100
From: Joerg Sonnenberger <joerg@britannica.bec.de>
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Subject: Re: assigning interrupts
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On Thu, Nov 13, 2008 at 08:56:31AM -0800, Jeremy Chadwick wrote:
> 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.

You still have a limited number of interrupt lines. Many non-highend
mainboards have 4 or 8 interrupt lines. You often have more than 8 PCI
devices that want interrupts (e.g. VGA, audio, 3 USB controllers, 1 EHCI
contoller and the SATA controller are enough to consume all lines).
As soon as you now add a new network devices, you end up sharing PCI
lines. The IO-APIC wiring is also often fixed, so it can't be controlled
by software.

Joerg