Re: Prevent IRQ sharing for PCI passthrough

[Avi Kivity <avi@redhat.com>]

On 05/13/2010 07:57 PM, Dirk Gouders wrote:
> Hello List,
>
> please don't shout at me if the answer to my question is too obvious,
>    

We won't shout at you.

> but in the German Linux Magazine I read an article about passing PCI
> devices to KVM guests and the authors said that "shared interrupt
> funcionality has to be disabled" which I read as "it is possible to
> disable shared interrupt functionality".
>    

It would be more correct to say "no go with shared host interrupts".

> I currently have the problem with a PCI ISDN card that is not MSI
> capable and even if I change the PCI slot and disable all other slots,
> USB etc. in the BIOS, that card still shares its interrupt with three
> other devices.
>
> Even after extensive searching/reading, I am not sure if it possible to
> prevent a PCI card from sharing an interrupt with other devices or
> probably manually assign a free interrupt to that card via some kernel
> parameter and would be glad if someone could give me an answer to that
> question.
>    

There is an ACPI _SRS method which can be used to move interrupts 
around.  However Linux doesn't appear to expose it.  Even if it did, the 
interrupt may be shared on the motherboard, in which case nothing would 
help (though you might be able to share it with unused devices).

Chris?

-- 
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