Re: ARM Snapshots Not Backwards-Compatible

[Aaron Lindsay]

On Feb 03 13:44, Andrew Jones wrote:
> On Wed, Feb 03, 2021 at 10:52:59AM +0000, Peter Maydell wrote:
> > On Wed, 3 Feb 2021 at 10:49, Dr. David Alan Gilbert <dgilbert@redhat.com> 
> > wrote:
> > >
> > > * Peter Maydell (peter.maydell@linaro.org) wrote:
> > > > On Wed, 3 Feb 2021 at 10:28, Dr. David Alan Gilbert 
> > > > <dgilbert@redhat.com> wrote:
> > > > >
> > > > > * Philippe Mathieu-Daudé (philmd@redhat.com) wrote:
> > > > > > Cc'ing migration team and qemu-arm@ list.
> > > > >
> > > > > I'll have to leave the detail of that to the ARM peole; but from a
> > > > > migration point of view I think we do want the 64 bit ARM migrations 
> > > > > to
> > > > > be stable now.  Please tie incompatible changes to machine types.
> > > >
> > > > That is the intention, but because there's no upstream testing
> > > > of migration compat, we never notice if we get it wrong.
> > > > What is x86 doing to keep cross-version migration working ?
> > >
> > > I know there used to be some of our team running Avocado tests for
> > > compatibility regularly, I'm not sure of the current status.
> > > It's something we also do regularly around when we do downstream
> > > releases, so we tend to catch them then, although even on x86 that
> > > often turns out to be a bit late.
> > 
> > So downstream testing only?
> 
> Not even downstream for the Arm architecture, at least not at Red Hat. The
> support we have for Arm Virt is still limited to the use cases for which
> it has been deployed. To this day that hasn't included migration[*].
> 
> > I think that unless we either (a) start
> > doing migration-compat testing consistently upstream or
> 
> This is the best choice and it can certainly be an additional approach
> regardless of what goes on downstream. I can look into this. A pointer
> to the x86 tests would be a good start. It's pretty simple to do a
> quick migration test between two versions of QEMU, but we need the
> whole build two versions of QEMU stuff first, which I hope already
> exists.

Does this mean that this is largely an issue of developing the tests,
and not a need for a place to host them? Or would additional
hardware/hosting be required for these tests to be run on?

-Aaron