Re: [Xen-devel] FW: about VIRQ & PIRQ

["pradeep singh rautela" <rautelap@xxxxxxxxx>]

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Hi Mark,
[snip]
> If I recall correctly, PIRQs are mapped one-to-one onto the lower numbered
> event channels (I'm not sure if this is specific to XenLinux or part of the
> Xen API).
>
> A VIRQ is a interrupt-like event that originates from Xen itself.  An example
> would be notifications from the Xen virtual timer device.  Again, the guest
> sees it as an event channel notification but this time we call it a VIRQ to
> show that it comes from an entirely *virtual* source.
Does this means if hypervisor recieves an interrupt from an external
card on the behalf of a domU, it actually buffers it like a an APIC
before eventually generating a VIRQ to the respective domU?

The above question is more obvious when we have an external hardware
device which generates interrupts are a very high rate e.g a busy
network card.

So, does Xen buffers the recieved IRQs if it is unable to send the IRQ
to the correct domU?

I hope same holds true while handling interrupts on the behalf of dom0.
Or is it that, Xen just forwards the interrupt to dom0 which then
handles the actual creation of a VIRQ using event channels to notify a
domU?

Thank you
- --psr

> There are actually more variations to event channels: events might also come
> from another domain we are communicating with, or (I think) from another VCPU
> in the same domain.
>
> Hope this helps,
> Cheers,
> Mark
>
> --
> Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
> Mark: To answer a question with a question: What use is a skateboard?
> Dave: Skateboards have wheels.
> Mark: My wheel has a wheel!
>
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pradeep singh rautela

"Genius is 1% inspiration, and 99% perspiration" - not me :)

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