Re: [Xen-devel] dom0 kernel - irq nobody cared ... the continuing saga ..

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.02.15 at 11:03, <linux@xxxxxxxxxxxxxx> wrote:
> Tuesday, February 10, 2015, 10:35:36 AM, you wrote:
>> I suppose that's because there's no handler installed by pciback, yet
>> IRQs generated by the passed through device also arrive in Dom0,
>> and the driver for the device left in Dom0 doesn't claim the interrupts.
> 
> Yes so just for my idea of what happened (and i have googled):
> the irq arrived at dom0 .. it went through the registered handlers:
> [ 1906.422483] handlers:
> [ 1906.441717] [<ffffffff8155cd42>] ata_bmdma_interrupt
> 
> In this case .. there is only one .. the handler verifies if it should
> actually handle this irq by the dev_id cookie, in this case it doesn't
> .. there are no handlers .. so after 200000 of those linux says hey we
> have an interrupt that nobody cared about.
> 
> So there is a chance it's an irq that was actually destined to the device
> that was passed through, but that didn't handle it ?
> If that's the case .. why .. wasn't it handled in time .. or was it shutdown 
> .. 
> or ...

No - such a shared IRQ gets sent to both domains. There's no notion
of one domain claiming it and the other then not seeing it, as any
instance of the interrupt may mean more than one of the devices
signaled it - remember that shared interrupts are always level
triggered, i.e. there is no way of telling how many devices request
servicing.

Jan


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