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Re: [Qemu-devel] [PATCH] pc: Clean up PIC-to-APIC IRQ path

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH] pc: Clean up PIC-to-APIC IRQ path
Date: Sun, 04 Sep 2011 08:57:31 -0500
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On 09/04/2011 08:49 AM, Jan Kiszka wrote:
On 2011-09-04 15:41, Anthony Liguori wrote:
On 09/04/2011 08:36 AM, Jan Kiszka wrote:
On 2011-09-04 15:32, Anthony Liguori wrote:
I prefer to not think of IRQs as special things.  They're just single
bits of information that flow through the device model.  Having a higher
level representation that understands something like paths seems wrong
to me.

I'd prefer to treat things like device assignment as a hack.  You just
need code that can walk the device tree to figure out the path (which is
not generic code, it's very machine specific).  Then you tell the kernel
the resolution of the path and are otherwise completely oblivious in

See it as you like, but we need the support, not only for device
assigment. And I do not see any gain it hacking this instead of
designing it.

You can design a hack but it's still a hack.

Device state belongs in devices.  Trying to extract device state
(interrupt routing paths) and externalizing it is by definition a hack.

Having some sort of global interrupt routing table is just going to add
a layer of complexity for very little obvious gain.

It's not yet decided how the problem is solved. A global interrupt
matrix is just one proposal, another option is to extend the pin model
in a way that supports routing change notifiers and backward polling.

If that's all you need, then you really just want notification on socket changes. Backwards polling can be achieved by just adding state to the Pin (which I full heartedly support).

If that's all you're proposing, than I'm entirely happy with it :-)

I'm happy with that because all of the route detection logic can live outside of the devices which at least contains the complexity.


Anthony Liguori

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