Re: [PATCH] hw/i386/pc_piix: Mark the machine types from version 1.4 to 1.7 as deprecated

[Philippe Mathieu-Daudé]

On 18/1/22 09:49, Thomas Huth wrote:
> On 17/01/2022 21.12, Daniel P. Berrangé wrote:
> > On Mon, Jan 17, 2022 at 08:16:39PM +0100, Thomas Huth wrote:
> > > The list of machine types grows larger and larger each release ... and
> > > it is unlikely that many people still use the very old ones for live
> > > migration. QEMU v1.7 has been released more than 8 years ago, so most
> > > people should have updated their machines to a newer version in those
> > > 8 years at least once. Thus let's mark the very old 1.x machine types
> > > as deprecated now.
> >
> > What criteria did you use for picking v1.7 as the end point ?
>
> I picked everything starting with a "1." this time ;-)
>
> No, honestly, since we don't have a deprecation policy in place yet, 
> there was no real good criteria around this time. For the machine types 
> < 1.3 there was a bug with migration, so these machine types could not 
> be used for reliable migration anymore anyway. But for the newer machine 
> types, we likely have to decide by other means indeed.
>
> > I'm fine with the idea of aging out machine types, but I'd like us
> > to explain the criteria we use for this, so that we can set clear
> > expectations for users. I'm not a fan of adhoc decisions that have
> > different impact every time we randomly decide to apply them.
> >
> > A simple rule could be time based - eg we could say
> >
> >    "we'll keep machine type versions for 5 years or 15 releases."
> >
> > one factor is how long our downstream consumers have been keeping
> > machines around for.
> >
> > In RHEL-9 for example, the oldest machine is "pc-i440fx-rhel7.6.0"
> > which IIUC is derived from QEMU 2.12.0. RHEL-9 is likely to rebase
> > QEMU quite a few times over the coming years, so that 2.12.0 version
> > sets an example baseline for how long machines might need to live for.
> > That's 4 years this April, and could potentially be 6-7 years by the
> > time RHEL-9 stops rebasing QEMU.
>
> Yeah, 5 years still seemed a little bit short to me, that's one of the 
> reasons why I did not add more machine types in my patch here. I think 
> with 7 or 8 years, we should be on the safe side.
>
> Any other opinions? And if we agree on an amount of years, where should 
> we document this? At the top of docs/about/deprecated.rst?

I suppose x86 being the oldest, x86 maintainers have to comment, but
5 years should be enough from sysadmins to migrate their VMs, isn't it?
(No need to migrate from 1 -> 8, they can do 1 -> 3 -> 5 -> 8, right?)

Anyhow you are right, better is to clearly state that in deprecated.rst,
at least to start and widen the discussion.