Re: [Qemu-devel] change x86 default machine type to Q35?

[Marcel Apfelbaum]

On 05/07/2017 11:14, Thomas Huth wrote:
>   Hi,

Hi,

> On 05.07.2017 08:57, Chao Peng wrote:
> > Q35 has been in QEMU for quite a while. Compared to the current default
> > i440FX, Q35 is probably not that mature and not widely used, however in
> > some case, Q35 has advantages, for example, in supporting new features.
> > For instance, we have some features require PCI-e support which is only
> > available on Q35 and some others need it for EFI support. It is of
> > course not necessary to change it as the default but if more and more
> > features have dependencies on Q35 because of requiring much more modern
> > features then I think it may be worth to do so. In such case we can have
> > more people to use it and find problems we may know or not know.

Agreed

> Yes, IMHO at one point in time, we should switch the default machine
> type to q35.

+1

> The i440FX is really quite old...
>
> > There are certainly some drawbacks:
> > -        Compatibility: current code or script may need adjustment
>
> That might be a real concern ... 

I am not so sure about that. Developers working on upstream projects
should expect such changes and, for our case,
modifying the command line by adding "-M pc" should not be a big deal.

The upper layers should manage the defaults by themselves so
are not supposed to be affected.

> so I think a good point in time to
> switch to the q35 machine type would be when we switch to the next major
> version number of QEMU, i.e. when we switch to version 3.0.

It does seem a good opportunity.

 If the users
> see a new major version number, they might be more willing to accept
> such major changes (yeah, I know, we've discussed in the past that
> version numbers are just numbers ... but still, there is some kind of
> psychological aspect to this, too, I think)
>
> > -        Quality: we may suffer more bugs on Q35
> > I hope that the q35 machine will become mature soon once it has been
> made the default machine.

It will certainly help, the question is the cost.
Exposing the bugs by having more developers working on Q35 looks
more like an opportunity then a "cost"  to me.

Thanks,
Marcel

>   Thomas