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Re: [Qemu-devel] Asynchronous / synchronous IO emulation

From: Dong, Eddie
Subject: Re: [Qemu-devel] Asynchronous / synchronous IO emulation
Date: Fri, 25 Nov 2016 09:17:08 +0000

> On Thu, Nov 24, 2016 at 08:44:06AM +0000, Dong, Eddie wrote:
> >          Under certain situation, we have a requirement to apply the
> virtual DMA event in a deterministic way. Current Qemu uses asynchronous
> approach to emulate the virtual IO events since quite long time ago. I am
> wondering if we still have an option to choose the synchronous emulation
> solution.
> Please explain exactly what you mean.
The usage is to construct a secondary hot standby VM (SVM), identical with the 
primary VM (PVM).
When an virtual DMA happens in PVM side, we need to know at which instruction 
boundary the virtual DMA is delivered, so that we can replay the virtual DMA 
event at the 2nd VM side, to keep them identical at any time.

Asynchronous IO emulations seems to be a little bit more complicate to be 
I might be wrong.

Thx Eddie

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