Re: [PATCH] target/ppc/cpu-models: Update max alias to power10

[Murilo Opsfelder Araújo]

Hi, Greg.

On 6/1/22 05:38, Greg Kurz wrote:
> On Wed, 1 Jun 2022 09:27:31 +0200
> Thomas Huth <thuth@redhat.com> wrote:
>
> > On 31/05/2022 19.27, Murilo Opsfelder Araujo wrote:
> > > Update max alias to power10 so users can take advantage of a more
> > > recent CPU model when '-cpu max' is provided.
> > >
> > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1038
> > > Cc: Daniel P. Berrangé <berrange@redhat.com>
> > > Cc: Thomas Huth <thuth@redhat.com>
> > > Cc: Cédric Le Goater <clg@kaod.org>
> > > Cc: Daniel Henrique Barboza <danielhb413@gmail.com>
> > > Cc: Fabiano Rosas <farosas@linux.ibm.com>
> > > Signed-off-by: Murilo Opsfelder Araujo <muriloo@linux.ibm.com>
> > > ---
> > >    target/ppc/cpu-models.c | 3 ++-
> > >    1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/target/ppc/cpu-models.c b/target/ppc/cpu-models.c
> > > index 976be5e0d1..c15fcb43a1 100644
> > > --- a/target/ppc/cpu-models.c
> > > +++ b/target/ppc/cpu-models.c
> > > @@ -879,7 +879,6 @@ PowerPCCPUAlias ppc_cpu_aliases[] = {
> > >        { "755", "755_v2.8" },
> > >        { "goldfinger", "755_v2.8" },
> > >        { "7400", "7400_v2.9" },
> > > -    { "max", "7400_v2.9" },
> > >        { "g4",  "7400_v2.9" },
> > >        { "7410", "7410_v1.4" },
> > >        { "nitro", "7410_v1.4" },
> > > @@ -910,6 +909,8 @@ PowerPCCPUAlias ppc_cpu_aliases[] = {
> > >        { "power8nvl", "power8nvl_v1.0" },
> > >        { "power9", "power9_v2.0" },
> > >        { "power10", "power10_v2.0" },
> > > +    /* Update the 'max' alias to the latest CPU model */
> > > +    { "max", "power10_v2.0" },
> > >    #endif
> >
> > I'm not sure whether "max" should really be fixed alias in this list here?
> > What if a user runs with KVM on a POWER8 host - then "max" won't work this
> > way, will it?
> >
> > And in the long run, it would also be good if this would work with other
> > machines like the "g3beige", too (which don't support the new 64-bit POWER
> > CPUs), so you should at least mention in the commit description that this is
> > only a temporary hack for the pseries machine, I think.
>
> I didn't even know there was a "max" alias :-)

Me too.  :)

> This was introduced by commit:
>
> commit 3fc6c082e3aad85addf25d36740030982963c0c8
> Author: Fabrice Bellard <fabrice@bellard.org>
> Date:   Sat Jul 2 20:59:34 2005 +0000
>
>      preliminary patch to support more PowerPC CPUs (Jocelyn Mayer)
>
> This was already a 7400 model at the time. Obviously we've never
> maintained that and I hardly see how it is useful... As Thomas
> noted, "max" has implicit semantics that depend on the host.
> This isn't migration friendly and I'm pretty sure libvirt
> doesn't use it (Daniel ?)
>
> We already have the concept of default CPU for the spapr
> machine types, that is usually popped up to the newer
> CPU model that is going to be supported in production.
> This goes with a bump of the machine type version as
> well for the sake of migration. This seems a lot more
> reliable than the "max" thingy IMHO.

We can use the default CPU type of the sPAPR machine as the "-cpu
max".  That would be a safer choice, I think.

Cheers!

--
Murilo