Re: [Qemu-devel] [RFC PATCH 0/5] asynchronous migration state change handlers

[Anthony Liguori]

On 06/06/2012 07:27 PM, Alon Levy wrote:
> > > If there is an active VNC client
> > > then it is there as a result of a user choosing to use it, so it should
> > > be treated as part of the user experience and not as something external.
> > > The experience from ignoring this and choosing to treat the remote
> > > console as an unrelated part is bound to be suboptimal.
> >
> > Guest migration affects correctness!
> >
> > If the Spice client is slow (even due to network lag) in responding to your
> > flush message, you will disrupt the guest and potentially drop network
> > connections and/or cause lockup detectors to trigger.
>
> OK, you think any timeout here would be too large.

What would it's value be?

Migration is convergent and our downtime estimate is just that--an estimate. 
It's literally always a crap-shoot as to whether the actual migration will 
complete fast enough.

What do you propose the timeout to be?  1us?  Can you even do a round trip to a 
client in 1us?  50us?  I still question whether a round trip is feasible in that 
time period and you've blown away the default 30us time anyway.

Even 1us would be too much though.

Regards,

Anthony Liguori