Re: [Qemu-devel] [PATCH 3/10] Add bdrv_flush_all()

[Avi Kivity]

Anthony Liguori wrote:
> I'm actually liking bdrv_flush_all() less and less.  If there are any 
> outstanding IO requests, it will increase the down time associated 
> with live migration.  I think we definitely need to add a live save 
> handler that waits until there are no outstanding IO requests to 
> converge.  I'm concerned though that it's not totally unreasonable to 
> expect a guest to always have an IO request in flight.  

I/O requests should complete in milliseconds; I don't see them as 
increasing migration latency.

> That leads me to think that maybe we should be cancelling outstanding 
> requests, and somehow saving their state?

Migration is enough of a special case that we should avoid special cases 
within it as much as possible.

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