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Date: Wed, 26 May 2010 11:08:14 +0300
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [Qemu-devel] Re: [RFT][PATCH 07/15] qemu_irq: Add IRQ handlers
	with delivery feedback
Message-ID: <20100526080814.GB2618@redhat.com>
References: <cover.1274732025.git.jan.kiszka@web.de>
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To: Jan Kiszka <jan.kiszka@web.de>
Cc: Blue Swirl <blauwirbel@gmail.com>, qemu-devel@nongnu.org, Juan Quintela <quintela@redhat.com>

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.