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Re: [PATCH v2 01/27] migration: Network Failover can't work with a pause
From: |
Daniel P . Berrangé |
Subject: |
Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest |
Date: |
Wed, 2 Dec 2020 10:55:15 +0000 |
User-agent: |
Mutt/1.14.6 (2020-07-11) |
On Wed, Dec 02, 2020 at 11:51:05AM +0100, Juan Quintela wrote:
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > On Wed, Dec 02, 2020 at 05:31:53AM -0500, Michael S. Tsirkin wrote:
> >> On Wed, Dec 02, 2020 at 10:27:18AM +0000, Daniel P. Berrangé wrote:
> >> > On Wed, Dec 02, 2020 at 05:13:18AM -0500, Michael S. Tsirkin wrote:
> >> > > On Wed, Nov 18, 2020 at 09:37:22AM +0100, Juan Quintela wrote:
> >> > > > If we have a paused guest, it can't unplug the network VF device, so
> >> > > > we wait there forever. Just change the code to give one error on
> >> > > > that
> >> > > > case.
> >> > > >
> >> > > > Signed-off-by: Juan Quintela <quintela@redhat.com>
> >> > >
> >> > > It's certainly possible but it's management that created
> >> > > this situation after all - why do we bother to enforce
> >> > > a policy? It is possible that management will unpause immediately
> >> > > afterwards and everything will proceed smoothly.
> >> > >
> >> > > Yes migration will not happen until guest is
> >> > > unpaused but the same it true of e.g. a guest that is stuck
> >> > > because of a bug.
> >> >
> >> > That's pretty different behaviour from how migration normally handles
> >> > a paused guest, which is that it is guaranteed to complete the migration
> >> > in as short a time as network bandwidth allows.
> >> >
> >> > Just ignoring the situation I think will lead to surprise apps / admins,
> >> > because the person/entity invoking the migration is not likely to have
> >> > checked wether this particular guest uses net failover or not before
> >> > invoking - they'll just be expecting a paused migration to run fast and
> >> > be guaranteed to complete.
> >> >
> >> > Regards,
> >> > Daniel
> >>
> >> Okay I guess. But then shouldn't we handle the reverse situation too:
> >> pausing guest after migration started but before device was
> >> unplugged?
> >>
> >
> > Thinking of which, I have no idea how we'd handle it - fail
> > pausing guest until migration is cancelled?
> >
> > All this seems heavy handed to me ...
>
> This is the minimal fix that I can think of.
>
> Further solution would be:
> - Add a new migration parameter: migrate-paused
> - change libvirt to use the new parameter if it exist
> - in qemu, when we do start migration (but after we wait for the unplug
> device) paused the guest before starting migration and resume it after
> migration finish.
It would also have to handle issuing of paused after migration has
been started - delay the pause request until the nuplug is complete
is one answer.
> My understanding talking with Laine is that they use this functionality
> by default for migration, saving, etc, i.e. it is not an isolated case.
Yep, save-to-disk always runs in the paused state, and migration is
also paused by default unless the mgmt app explicitl asks for live
migration.
Regards,
Daniel
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- Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest, Michael S. Tsirkin, 2020/12/02
- Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest, Daniel P . Berrangé, 2020/12/02
- Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest, Michael S. Tsirkin, 2020/12/02
- Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest, Michael S. Tsirkin, 2020/12/02
- Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest, Juan Quintela, 2020/12/02
- Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest,
Daniel P . Berrangé <=
- Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest, Michael S. Tsirkin, 2020/12/02
- Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest, Daniel P . Berrangé, 2020/12/02
- Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest, Michael S. Tsirkin, 2020/12/02
- Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest, Daniel P . Berrangé, 2020/12/02
- Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest, Michael S. Tsirkin, 2020/12/03
- Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest, Daniel P . Berrangé, 2020/12/03
- Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest, Michael S. Tsirkin, 2020/12/03
- Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest, Dr. David Alan Gilbert, 2020/12/03
- Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest, Michael S. Tsirkin, 2020/12/03
- Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest, Dr. David Alan Gilbert, 2020/12/03