On Thu, Dec 03, 2020 at 06:21:47AM -0500, Michael S. Tsirkin wrote: > On Wed, Dec 02, 2020 at 12:01:21PM +0000, Daniel P. Berrangé wrote: > > On Wed, Dec 02, 2020 at 06:37:46AM -0500, Michael S. Tsirkin wrote: > > > On Wed, Dec 02, 2020 at 11:26:39AM +0000, Daniel P. Berrangé wrote: > > > > On Wed, Dec 02, 2020 at 06:19:29AM -0500, Michael S. Tsirkin wrote: > > > > > On Wed, Dec 02, 2020 at 10:55:15AM +0000, Daniel P. Berrangé wrote: > > > > > > 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. > > > > > > > > > > Hmm my worry would be that pausing is one way to give cpu > > > > > resources back to host. It's problematic if guest can delay > > > > > that indefinitely. > > > > > > > > hmm, yes, that is awkward. Perhaps we should just report an explicit > > > > error then. > > > > > > Report an error in response to which command? Do you mean > > > fail migration? > > > > If mgt attempt to pause an existing migration that hasn't finished > > the PCI unplug stage, then fail the pause request. > > Pause guest not migration ... > Might be tricky ... > > Let me ask this, why not just produce a warning > that migration wan't finish until guest actually runs? > User will then know and unpause the guest when he wants > migration to succeed ...
A warning is going to be essentally invisible if the pause command succeeeds. 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 :|
