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

[Avi Kivity]

On 09/04/2011 04:41 PM, Anthony Liguori wrote:
> > 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.

Pet peeve - saying something is "by definition" a hack is just rhetoric 
unless the definition of device state is "something that cannot be 
extracted and externalized".  Let's avoid this.

In fact it's exactly what we do with the memory API.  Memory routing is 
part of device state, yet we expose it to the memory API and let it do 
its thing instead of going through the hierarchy on every single memory 
access.

Whether it's worthwhile to do this for interrupts as well depends on how 
common the situation is and what we gain from it.  We can only do this 
if the routing is semi-static (depends only on other state but not the 
actual interrupt) - probably the only exception to this is the "least 
priority" mode which means the last leg cannot be computed statically.

I agree the gain is low if we limit ourselves to 440fx, but if we add 
interrupt remapping it becomes considerably more complicated to do this 
backward path computation.

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