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

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

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On 6/6/07, Petersson, Mats  wrote:
[snip]
> > 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?
>
>
> Yes, essentially so. There is a bitmap for each guest of "pending
> interrupts", which is read based on an event to the guest.
>
> >
> > 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?
>
> It is "never unable" to send the IRQ to the guest. The guest may be
> unable to TAKE the interrupt at this point, but it's never unable for
> the hypervisor to "send" the IRQ to the guest.
Yes, messed that up here.
> To understand better, have a look at .../xen/arch/x86/irq.c, and in
> particular the function __do_IRQ_guest().
>
> >
> > 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?
>
> I think I've told you before, Dom0 is no different from any other domain
> when it comes to how it interacts with the hypervisor, aside from having
> a bit set that says "You're allowed to do things like
> creating/destroying other guests". Interrupt handling in Dom0 is exactly
> identical to any other guest - there is nothing in the above irq.c file
> that says "if (domain is dom0) ..." (in fact, the only domain_id usage
> is for a printk in the "dump_irqs" function, which is for dumping the
> current IRQ state on the console when in Xen console-mode.
Thank you Mats.

Regards
- --psr
> --
> Mats
> >
> > 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!
> > >
> > > _______________________________________________
> > > Xen-devel mailing list
> > > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > > http://lists.xensource.com/xen-devel
> > >
> >
> >
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> > --
> > ---
> > pradeep singh rautela
> >
> > "Genius is 1% inspiration, and 99% perspiration" - not me :)
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel
> >
> >
> >

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--
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pradeep singh rautela

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

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