Hello Jiri, On Thursday 29 August, 2024 at 04:58:39 pm IST, Jiri Denemark <jdenemar@redhat.com> wrote:
* Does the same waiting happen when using options (2) and (3) above?
No. The explicit "virsh migrate-postcopy" request expects the user to decide when to switch to post-copy by monitoring the migration.
* While running migration tests switch to postcopy appears to happen within 2 seconds of starting migration. - Is that reasonable time to switch from pre-copy to postcopy?
No, that's not very reasonable. Basically every memory page access would have to be delayed until the page is transferred from the source host.
- Is there an ideal time to wait before switching to postcopy?
Not really. As the name suggests this is meant as a timeout, i.e., switch to post-copy if pre-copy migration is taking too long and thus is unlikely to ever converge. So logically the timeout should be long enough to give pre-copy migration to do its job. In this case, switching to post-copy is an alternative approach to CPU throttling for helping migration to converge.
* The feature page below suggests to wait until one cycle of RAM migration has completed -> https://wiki.qemu.org/Features/PostCopyLiveMigration
Right, that's definitely a good approach as only memory pages that changed during migration will have to be transferred from the source.
* Okay, great! Thanks so much for these details, I appreciate it. Thank you. --- - Prasad