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Re: [Xen-devel] Interrupt to CPU routing in HVM domains - again

To: John Levon <levon@xxxxxxxxxxxxxxxxx>, Steve Ofsthun <sofsthun@xxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Interrupt to CPU routing in HVM domains - again
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Sat, 06 Sep 2008 08:48:32 +0100
Cc: James Harper <james.harper@xxxxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, bart brooks <bart_brooks@xxxxxxxxxxx>
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Thread-topic: [Xen-devel] Interrupt to CPU routing in HVM domains - again
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On 5/9/08 18:28, "John Levon" <levon@xxxxxxxxxxxxxxxxx> wrote:

>> Our driver writers would like to see support for multiple callback IRQs.
>> Then particular event channel interrupts could be bound to particular IRQs.
>> This would allow PV device interrupts to be distributed intelligently.  It
>> would also allow net and block interrupts to be disentangled for Windows PV
>> drivers.
> You could do a bunch of that just by distributing them from the single
> callback IRQ. But I suppose it would be nice to move to a
> one-IRQ-per-evtchn model. You'd need to keep the ABI of course, so you'd
> need a feature flag or something.

Yes, it should work as follows:
one-IRQ-per-evtchn and turn off the usual PV per-VCPU selector word and
evtchn_pending master flag (as we have already disabled the evtchn_mask
master flag). Then all evtchn re-routing would be handled through the
IO-APIC like all other emulated IRQs.

I'd consider a clean patch to do this (would need to be backward compatible
with old PV-on-HVM drivers). I won't take hacks of the sort Steve posted
(not that he expected me to!).

 -- Keir

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