Re: [PATCH v3 1/7] migration: Add switchover ack capability

[Peter Xu]

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 <avihaih@nvidia.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu