Re: [PATCH 1/8] migration: Add precopy initial data capability

[Juan Quintela]

Avihai Horon <avihaih@nvidia.com> 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 "precopy initial data" that allows the
> source to send initial precopy data and the destination to ACK that this
> data has been loaded. Migration will not attempt to stop the source VM
> and complete the migration until this ACK is received.
>
> This will allow migration users to send initial precopy data which can
> be used to reduce downtime (e.g., by pre-allocating resources), while
> making sure that the source will stop the VM and complete the migration
> only after this initial precopy data is sent and loaded in the
> destination 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>


Capability definition is correct.
I am not given the review-by until the rest of the series is discussed,
but nothing else to do here.