On Sun, May 21, 2023 at 06:18:02PM +0300, Avihai Horon wrote: > Migration downtime estimation is calculated based on bandwidth and > remaining migration data. This assumes that loading of migration data in > the destination takes a negligible amount of time and that downtime > depends only on network speed. > > While this may be true for RAM, it's not necessarily true for other > migration users. For example, loading the data of a VFIO device in the > destination might require from the device to allocate resources, prepare > internal data structures and so on. These operations can take a > significant amount of time which can increase migration downtime. > > This patch adds a new capability "switchover ack" that prevents the > source from stopping the VM and completing the migration until an ACK > is received from the destination that it's OK to do so. > > This can be used by migrated devices in various ways to reduce downtime. > For example, a device can send initial precopy metadata to pre-allocate > resources in the destination and use this capability to make sure that > the pre-allocation is completed before the source VM is stopped, so it > will have full effect. > > This new capability relies on the return path capability to communicate > from the destination back to the source. > > The actual implementation of the capability will be added in the > following patches. > > Signed-off-by: Avihai Horon <avih...@nvidia.com>
Reviewed-by: Peter Xu <pet...@redhat.com> -- Peter Xu
