[Qemu-devel] Re: Live migration broken when under heavy IO

[Avi Kivity]

On 06/16/2009 03:50 PM, Anthony Liguori wrote:
> Avi Kivity wrote:
> > > Does anyone have a clever idea how to fix this without just waiting 
> > > for all IO requests to complete?
> >
> > What's wrong with waiting for requests to complete?  It should take a 
> > few tens of milliseconds.
>
> An alternative would be to attempt to cancel the requests.  This 
> incurs no non-deterministic latency.

Yes, that's even better (though without linux-aio, it's equivalent).

> The tricky bit is that this has to happen at the device layer because 
> the opaques cannot be saved in a meaningful way.

Do you mean the device has to record all cancelled requests and replay 
them?  I think we can do it at the block layer (though we have to avoid 
it for nested requests).

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