On Wed, Dec 02, 2020 at 11:51:05AM +0100, Juan Quintela wrote: > "Michael S. Tsirkin" <m...@redhat.com> wrote: > > On Wed, Dec 02, 2020 at 05:31:53AM -0500, Michael S. Tsirkin wrote: > >> On Wed, Dec 02, 2020 at 10:27:18AM +0000, Daniel P. Berrangé wrote: > >> > On Wed, Dec 02, 2020 at 05:13:18AM -0500, Michael S. Tsirkin wrote: > >> > > On Wed, Nov 18, 2020 at 09:37:22AM +0100, Juan Quintela wrote: > >> > > > If we have a paused guest, it can't unplug the network VF device, so > >> > > > we wait there forever. Just change the code to give one error on > >> > > > that > >> > > > case. > >> > > > > >> > > > Signed-off-by: Juan Quintela <quint...@redhat.com> > >> > > > >> > > It's certainly possible but it's management that created > >> > > this situation after all - why do we bother to enforce > >> > > a policy? It is possible that management will unpause immediately > >> > > afterwards and everything will proceed smoothly. > >> > > > >> > > Yes migration will not happen until guest is > >> > > unpaused but the same it true of e.g. a guest that is stuck > >> > > because of a bug. > >> > > >> > That's pretty different behaviour from how migration normally handles > >> > a paused guest, which is that it is guaranteed to complete the migration > >> > in as short a time as network bandwidth allows. > >> > > >> > Just ignoring the situation I think will lead to surprise apps / admins, > >> > because the person/entity invoking the migration is not likely to have > >> > checked wether this particular guest uses net failover or not before > >> > invoking - they'll just be expecting a paused migration to run fast and > >> > be guaranteed to complete. > >> > > >> > Regards, > >> > Daniel > >> > >> Okay I guess. But then shouldn't we handle the reverse situation too: > >> pausing guest after migration started but before device was > >> unplugged? > >> > > > > Thinking of which, I have no idea how we'd handle it - fail > > pausing guest until migration is cancelled? > > > > All this seems heavy handed to me ... > > This is the minimal fix that I can think of. > > Further solution would be: > - Add a new migration parameter: migrate-paused > - change libvirt to use the new parameter if it exist > - in qemu, when we do start migration (but after we wait for the unplug > device) paused the guest before starting migration and resume it after > migration finish.
It would also have to handle issuing of paused after migration has been started - delay the pause request until the nuplug is complete is one answer. > My understanding talking with Laine is that they use this functionality > by default for migration, saving, etc, i.e. it is not an isolated case. Yep, save-to-disk always runs in the paused state, and migration is also paused by default unless the mgmt app explicitl asks for live migration. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
