Re: question on s390x topology: KVM only, or also TCG?

[Nina Schoetterl-Glausch]

On Thu, 2024-03-14 at 16:54 +0100, Thomas Huth wrote:
> On 14/03/2024 16.49, Claudio Fontana wrote:
> > Hello Pierre, Ilya,
> > 
> > I have a question on the s390x "topology" feature and examples.
> > 
> > Mainly, is this feature supposed to be KVM accelerator-only, or also 
> > available when using the TCG accelerator?
> 
>   Hi Claudio!
> 
> Pierre left IBM, please CC: Nina with regards to s390x topology instead.
> 
> But with regards to your question, I think I can answer that, too: The 
> topology feature is currently working with KVM only, yes. It hasn't been 
> implemented for TCG yet.
> 
> > (docs/devel/s390-cpu-topology.rst vs 
> > https://www.qemu.org/docs/master/system/s390x/cpu-topology.html)
> > 
> > I see stsi-topology.c in target/s390x/kvm/ , so that part is clearly 
> > KVM-specific,
> > 
> > but in hw/s390x/cpu-topology.c I read:
> > 
> > "
> >   * - The first part in this file is taking care of all common functions
> >   *   used by KVM and TCG to create and modify the topology.

What Thomas said. Read this as the code in file being independent with respect 
to the accelerator,
it's just that TCG support is missing.
 
[...]
> > 
> > So I would assume this is KVM-only, but then in the "Examples" section 
> > below I see the example:
> > 
> > "
> > $ qemu-system-s390x -m 2G \
> >    -cpu gen16b,ctop=on \

TCG doesn't support this cpu ^ and so will refuse to run.

> >    -smp cpus=5,sockets=8,cores=4,maxcpus=32 \

When running with TCG, drawers & books are supported by -smp also, but well, 
you cannot do anything
with that.

[...]
>