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

[Anthony Liguori <anthony@codemonkey.ws>]

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