Re: [Qemu-devel] [PATCH 00/46] Postcopy implementation

[Paolo Bonzini]

Il 07/07/2014 16:02, Dr. David Alan Gilbert ha scritto:
> > > Could you have instead a "migrate_start_postcopy" command, and leave the
> > > policy to management instead?
> Hmm; yes that is probably possible - although with the migration_set_parameter
> configuration you get the best of both worlds:
>    1) You can set the parameter to say a few seconds and let QEMU handle it
>    2) You can set the parameter really large, but (I need to check) you could
>       drop the parameter later and then cause it to kick in.
>
> I also did it this way because it was similar to the way the auto-throttling
> mechanism.

Auto-throttling doesn't let you configure when it kicks in (it doesn't 
even need support from the destination side).  For postcopy you would 
still have a capability, like auto-throttling, just not the argument.

The reason why I prefer a manual step from management, is because 
postcopy is a one-way street.  Suppose a newer version of management 
software has started migration with postcopy configured, and then an 
older version is started.  It is probably an invalid thing to do, but 
the confusion in the older version could be fatal and it's nice if 
there's an easy way to prevent it.

Paolo