On Thu, Sep 18, 2025 at 11:10:49AM -0400, Peter Xu wrote: > On Thu, Sep 18, 2025 at 03:45:21PM +0100, Daniel P. Berrangé wrote: > > There needs to be a way to initiate post-copy recovery regardless > > of whether we've hit a keepalive timeout. Especially if we can > > see one QEMU in postcopy-paused, but not the other side, it > > doesn't appear to make sense to block the recovery process. > > > > The virDomainJobCancel command can do a migrate-cancel on the > > src, but it didn't look like we could do the same on the dst. > > Unless I've overlooked something, Libvirt needs to gain a way > > to explicitly force both sides into the postcopy-paused state, > > and thus be able to immediately initiate recovery. > > Right, if libvirt can do that then problem should have been solved too. > > > I'm fine with turning on keepalives on the socket, but IMHO the > > out of the box behaviour should be to honour the kernel default > > tunables unless the admin decides they want different behaviour. > > I'm not seeing a rational for why the kernel defaults should be > > forceably overridden in QEMU out of the box. > > IMHO the rational here is that the socket here is in a special state and > for special purpose. So we're not trying to change anything globally for > qemu (without knowing what the socket is), but only this specific type of > socket that is used for either precopy or postcopy live migrations. > > It's special because it's always safe to have a more aggresive > disconnection, and might be preferred versus very lengthy hangs (if > assuming libvirt doesn't yet have way to stop the hang), especially for a > postcopy phase.
I've already described up-thread that it is not guaranteed safe to have aggressive disconnection. It is often safe, but there is definitely non-negligible risk in prematurely terminating a migration connection. With 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 :|
