Re: [Qemu-devel] [RFC PATCH 1/3] target-i386: Add 486sx, old486, and old486sx CPU models

[Eduardo Habkost]

On Mon, Mar 25, 2013 at 11:44:30AM -0700, H. Peter Anvin wrote:
> On 03/25/2013 08:15 AM, Igor Mammedov wrote:
> >>
> >> Such changes have been rejected in the past (e.g., n270 Atom).
> >> I personally wouldn't object to 486 changes, but I guess it should
> >> rather be handled via Igor's CPU static properties that I have in my
> >> review queue: The .model value would be set to 8 but the PC machine
> >> would be changed alongside to set model = 0 for pc-1.4 and earlier.
> > It doesn't relates to property refactoring nor to slim CPU sub-classes
> > conversion either. So it could go in independently.
> > 
> > But is this change safe from migration POV?
> > 
> 
> Well, given that the CPU model presented is actually closer to a model 8
> than a model 0 it probably is... but the real question is what would
> cause someone to do migration of a 486 CPU model.
> 
> The n270 issue is problematic, because right now "n270" can't actually
> run software compiled for N270...

FWIW, I wouldn't mind too much if the maintainers decide to document 486
and n270 as "migration-unsafe" and then knowingly break live-migration
of those CPU models between qemu <= 1.3 and qemu >= 1.4. It's up to the
maintainers to choose which way to go.

-- 
Eduardo