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

From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] Asynchronous / synchronous IO emulation
Date: Fri, 25 Nov 2016 12:01:10 +0000
User-agent: Mutt/1.7.1 (2016-10-04)

On Fri, Nov 25, 2016 at 09:17:08AM +0000, Dong, Eddie wrote:
> > 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 
> deterministic...
> I might be wrong.

There is a record-replay mode that might be worth investigating.  See

It sounds like you are not using live migration for micro-checkpoints?
The live migration mechanism would keep memory in sync at each

Is this work releated to the COLO effort?


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