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Date: Sun, 30 May 2010 14:52:59 +0300
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [Qemu-devel] Re: [RFT][PATCH 07/15] qemu_irq: Add IRQ handlers
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To: Blue Swirl <blauwirbel@gmail.com>
Cc: Jan Kiszka <jan.kiszka@web.de>, qemu-devel@nongnu.org, Juan Quintela <quintela@redhat.com>

On Sun, May 30, 2010 at 11:41:36AM +0000, Blue Swirl wrote:
> >> I meant that in the scenario, the guest won't change the RTC before
> >> 30Mcyc because of some built in determinism in the guest. At that
> >> point, because of some reason, the change would happen.
> >>
> > I still don't understand what are you trying to say here. Guest changes
> > frequency because of some even in the guest. It is totally independent
> > of what happens in QEMUs RTC emulation.
> 
> I'm trying to understand the order of events. In the scenario, the
> order of events on real HW would be:
> 10Mcyc: tick IRQ 1
> 20Mcyc: tick IRQ 2
> 30Mcyc: tick IRQ 3
> 30Mcyc: reprogram timer
> 31Mcyc: tick IRQ 4
> 32Mcyc: tick IRQ 5
> 33Mcyc: tick IRQ 6
> 34Mcyc: tick IRQ 7
> 
> With QEMU, the order could become:
> 30Mcyc: reprogram timer
> 30.5Mcyc: tick IRQ 1
> 31Mcyc: tick IRQ 2
> 31.5Mcyc: tick IRQ 3
> 32Mcyc: tick IRQ 4
> 32.5Mcyc: tick IRQ 5
> 33Mcyc: tick IRQ 6
> 34Mcyc: tick IRQ 7
> 
> Correct?
Not sure, your description is not complete. Let me try:
On real HW:
10Mcyc: tick IRQ 1 -> delivered to an OS
20Mcyc: tick IRQ 2 -> delivered to an OS
30Mcyc: tick IRQ 3 -> delivered to an OS
30Mcyc: reprogram timer
31Mcyc: tick IRQ 4 -> delivered to an OS
32Mcyc: tick IRQ 5 -> delivered to an OS
33Mcyc: tick IRQ 6 -> delivered to an OS
34Mcyc: tick IRQ 7 -> delivered to an OS

With QEMU:
10Mcyc: tick IRQ 1 -> coalesced
20Mcyc: tick IRQ 2 -> coalesced
30Mcyc: tick IRQ 3 -> coalesced
30Mcyc: reprogram timer
30.1Mcyc: tick IRQ 1 -> delivered to an OS
30.2Mcyc: tick IRQ 2 -> delivered to an OS
30.3Mcyc: tick IRQ 3 -> delivered to an OS
31Mcyc: tick IRQ 4 -> delivered to an OS
32Mcyc: tick IRQ 5 -> delivered to an OS
33Mcyc: tick IRQ 6 -> delivered to an OS
34Mcyc: tick IRQ 7 -> delivered to an OS



--
			Gleb.