Re: [Qemu-devel] Re: [RFT][PATCH 07/15] qemu_irq: Add IRQ handlers with delivery feedback

[Gleb Natapov]

On Tue, May 25, 2010 at 11:44:50PM +0200, Jan Kiszka wrote:
> > 
> >> I think the real solution to coalescing is put the logic inside one
> >> device, in this case APIC because it has the information about irq
> >> delivery. APIC could monitor incoming RTC irqs for frequency
> >> information and whether they get delivered or not. If not, an internal
> >> timer is installed which injects the lost irqs.
> 
> That won't fly as the IRQs will already arrive at the APIC with a
> sufficiently high jitter. At the bare minimum, you need to tell the
> interrupt controller about the fact that a particular IRQ should be
> delivered at a specific regular rate. For this, you also need a generic
> interface - nothing really "won".
> 
Not only that. Suppose RTC runs with 64Hz frequency and N interrupts
were coalesced during some period. Now the guest reprograms RTC to
1024Hz. N should be scaled accordingly otherwise reinjection will not
fix the drift. Do you propose to put this logic into APIC to?

--
                        Gleb.