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Re: [Xen-devel] Multiple IRQ's in HVM for Windows

  • To: James Harper <james.harper@xxxxxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
  • Date: Sun, 28 Dec 2008 08:39:00 +0000
  • Cc:
  • Delivery-date: Sun, 28 Dec 2008 00:39:34 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-topic: [Xen-devel] Multiple IRQ's in HVM for Windows

On 28/12/2008 03:22, "James Harper" <james.harper@xxxxxxxxxxxxxxxx> wrote:

>> Yes, that did occur to me. Might be a nice fallback while still
> allowing
>> up
>> to 16 or whatever devices to have their interrupts distributed across
>> VCPUs.
>> The old mechanism does still need to work, so making it a fallback in
> this
>> new mechanism would be probably not too difficult.
> I've been reading up on APIC's, and it appears that (depending on the
> model) they can support up to 64 interrupts. Is the emulated APIC under
> Xen of the 16 interrupt variety?

The IO-APIC has 48 pins, 16 of which are mapped for legacy ISA, so there are
32 non-legacy pins. Actually we could have more, but that creates
backward-compatibility issues now. 32 should be enough for most uses!

 -- Keir

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