Re: [Qemu-devel] [RFC V2, PATCH 0/2] Checkpoint-assisted migration proposal

[Bohdan Trach <bohdan.trach@mailbox.tu-dresden.de>]

Hi Eric,

On 11/24/2015 06:51 PM, Eric Blake wrote:
> This touches the command line, but not any QMP .json files.  Is this new
> feature properly discoverable using existing QMP commands, or is this
> something lacking in the proposal?

What exactly discoverability mechanisms must be provided?

The current workflow goes like this:
1. VM is started, works for some time. This will be the migration
   source.
2. A migration destination is started, with -checkpoint argument
   passed to it (even if the checkpoint file doesn't exist).
3. A migration happens. There is no way to enable checkpoint-assisted
   migration at this stage, even if checkpoint file is available. But
   the destination computes hashes of pages that it receives.
4. The VM that was migration destination will use checkpoint-assisted
   migration from now on.
5. A migration source pauses after migration, and creates a checkpoint
   using the dump-guest-memory command. The migration destination has
   hashes of pages that are in the checkpoint.

So the migration source uses checkpoint-assisted migration only if it
previously was migration destination with -checkpoint argument. The
very first migration always happens without checkpoint.  We can rework
this in the next revisions, if it's required. One option would not to
to store hashes in the migration destination, but to load the
checkpoint explicitly in the migration source before migration.

-- 
With best regards,
Bohdan Trach