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Re: -only-migrate and the two different uses of migration blockers (was:
From: |
Dr. David Alan Gilbert |
Subject: |
Re: -only-migrate and the two different uses of migration blockers (was: spapr_events: Sure we may ignore migrate_add_blocker() failure?) |
Date: |
Mon, 19 Jul 2021 13:42:57 +0100 |
User-agent: |
Mutt/2.0.7 (2021-05-04) |
* Markus Armbruster (armbru@redhat.com) wrote:
> We appear to use migration blockers in two ways:
>
> (1) Prevent migration for an indefinite time, typically due to use of
> some feature that isn't compatible with migration.
>
> (2) Delay migration for a short time.
>
> Option -only-migrate is designed for (1). It interferes with (2).
>
> Example for (1): device "x-pci-proxy-dev" doesn't support migration. It
> adds a migration blocker on realize, and deletes it on unrealize. With
> -only-migrate, device realize fails. Works as designed.
>
> Example for (2): spapr_mce_req_event() makes an effort to prevent
> migration degrate the reporting of FWNMIs. It adds a migration blocker
> when it receives one, and deletes it when it's done handling it. This
> is a best effort; if migration is already in progress by the time FWNMI
> is received, we simply carry on, and that's okay. However, option
> -only-migrate sabotages the best effort entirely.
That's interesting; it's the first time I've heard of anyone using it as
'best effort'. I've always regarded blockers as blocking.
> While this isn't exactly terrible, it may be a weakness in our thinking
> and our infrastructure. I'm bringing it up so the people in charge are
> aware :)
Thanks.
It almost feels like they need a way to temporarily hold off
'completion' of migratio - i.e. the phase where we stop the CPU and
write the device data; mind you you'd also probably want it to stop
cold-migrates/snapshots?
Dave
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
- spapr_events: Sure we may ignore migrate_add_blocker() failure?, Markus Armbruster, 2021/07/15
- Re: spapr_events: Sure we may ignore migrate_add_blocker() failure?, David Gibson, 2021/07/18
- Re: spapr_events: Sure we may ignore migrate_add_blocker() failure?, Markus Armbruster, 2021/07/19
- Re: spapr_events: Sure we may ignore migrate_add_blocker() failure?, David Gibson, 2021/07/19
- Re: spapr_events: Sure we may ignore migrate_add_blocker() failure?, Markus Armbruster, 2021/07/19
- -only-migrate and the two different uses of migration blockers (was: spapr_events: Sure we may ignore migrate_add_blocker() failure?), Markus Armbruster, 2021/07/19
- Re: -only-migrate and the two different uses of migration blockers (was: spapr_events: Sure we may ignore migrate_add_blocker() failure?),
Dr. David Alan Gilbert <=
- Re: -only-migrate and the two different uses of migration blockers, Markus Armbruster, 2021/07/20
- Re: -only-migrate and the two different uses of migration blockers, David Gibson, 2021/07/21
- Re: -only-migrate and the two different uses of migration blockers, Dr. David Alan Gilbert, 2021/07/22
- Re: -only-migrate and the two different uses of migration blockers, David Gibson, 2021/07/25
- Re: spapr_events: Sure we may ignore migrate_add_blocker() failure?, David Gibson, 2021/07/21