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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH 1/3] Change qemu_set_irq() to return status
	information.
Date: Mon, 30 Jun 2008 15:00:44 +0100
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To: qemu-devel@nongnu.org
Cc: Gleb Natapov <gleb@qumranet.com>

> I forgot to rebase my branch that is why grep showed nothing ;) But
> there is no much documentation about virtual time base. I can't see why
> this hack cannot coexist with virtual time base. If virtual time base
> somehow guaranties that interrupts will never be lost then qemu_irq_rase()
> will never return zero and the hack will be as good as disabled.

The virtual time base guarantees that a reasonable number of instruction will 
have been executed in a given virtual time period. Ticks can still be "lost" 
if the guest OS keeps the IRQ disable for a long time. However this behaviour 
matches that of real hardware, so they should not be reinserted later.

The only reason this is a problem with normal qemu is because the virtual CPU 
speed is extremely variable, and can stall for very long periods of time.

Paul