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From: Blue Swirl <blauwirbel@gmail.com>
Date: Mon, 7 Dec 2009 20:08:45 +0200
Message-ID: <f43fc5580912071008q1a072f29x27678ea69a7a5ee0@mail.gmail.com>
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Subject: [Qemu-devel] Re: irq latency and tcg
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To: Artyom Tarasenko <atar4qemu@googlemail.com>
Cc: qemu-devel <qemu-devel@nongnu.org>

On Mon, Dec 7, 2009 at 3:30 PM, Artyom Tarasenko
<atar4qemu@googlemail.com> wrote:
> Can it be that qemu (-system-sparc in my case, but I guess it's more
> or less similar on all platforms) reacts to irqs slower than a real
> hardware due to tcg optimizations?
>
> I see one test pattern which fails on qemu:
>
> <cause an interrupt>
> nop * N
> <check whether the interrupt happened>
>
> What I observe is that the proper interrupt does take a place, but
> after the check, so no-one expects it anymore.
> Is there a way to reduce the interrupt latency? Or maybe there is a
> good substitute to a nop*N, so that irq would definitely get through
> in the mean time?

On Sparc, nops do not generate any code at all.