Re: TARGET_CPUS in assign_irq_vector

From: Eric W. Biederman
Date: Wed Sep 10 2008 - 16:15:15 EST

Jeremy Fitzhardinge <jeremy@xxxxxxxx> writes:

> Hm. That would work OK for fully paravirtualized domains, which have no
> direct access to real hardware in any form (well, there's pci
> passthough, but interrupts are all thoroughly massaged into event channels).
> But for dom0, the kernel handles interrupts weird hybrid mode. The
> interrupts themselves are delivered via event channels rather than via a
> local apic, but the IO APIC is still under the kernel's control, and is
> responsible for poking (Xen-allocated) vectors into it. This only
> applies to physical irq event channels; there's no need to have vectors
> for purely software event channels like interdomain, IPI and timers.
> This is further complicated by the fact that the dom0 kernel parses the
> ACPI and MPTABLES to find out about IO APICs, so the existing APIC
> subsystem is already involved. I need to work out how'd I'd hook all
> this together with a minimum of mess.

In that case. Having the information on the event channel tell you
which cpu and which vector were received is sufficient. Then you
can call into do_IRQ() with the information. Unless ack_irq()
and friends are enough different at the local apic level to cause
a challenge.

For the reset of the event channel interrupts you simply want to
dispatch the irq directly.

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