Re: [PATCH v19 01/21] s390x/cpu topology: add s390 specifics to CPU topology

[Thomas Huth <thuth@redhat.com>]

On 18/04/2023 12.01, Pierre Morel wrote:
> 
> On 4/18/23 10:53, Nina Schoetterl-Glausch wrote:
>> On Mon, 2023-04-03 at 18:28 +0200, Pierre Morel wrote:
>>> S390 adds two new SMP levels, drawers and books to the CPU
>>> topology.
>>> The S390 CPU have specific topology features like dedication
>>> and entitlement to give to the guest indications on the host
>>> vCPUs scheduling and help the guest take the best decisions
>>> on the scheduling of threads on the vCPUs.
>>>
>>> Let us provide the SMP properties with books and drawers levels
>>> and S390 CPU with dedication and entitlement,
>>>
>>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>>> Reviewed-by: Thomas Huth <thuth@redhat.com>
>>> ---
>>>   MAINTAINERS                     |  5 ++++
>>>   qapi/machine-common.json        | 22 ++++++++++++++
>>>   qapi/machine-target.json        | 12 ++++++++
>>>   qapi/machine.json               | 17 +++++++++--
>>>   include/hw/boards.h             | 10 ++++++-
>>>   include/hw/s390x/cpu-topology.h | 15 ++++++++++
>> Is hw/s390x the right path for cpu-topology?
>> I haven't understood the difference between hw/s390x and target/s390x
>> but target/s390x feels more correct, I could be mistaken though.
> 
> AFAIK target/s390 is for CPU emulation code while hw/s390 is for other 
> emulation.
> 
> So it depends how we classify the CPU topology, it is related to CPU but it 
> is no emulation.

Normally I'd say target/ is for everything what happens within a CPU chip, 
and hw/ is for everything that happens outside of a CPU chip, i.e. machine 
definitions and other devices.
Now CPU topology is borderline - drawers and books are rather a concept of 
the machine and not of the CPU, but things like dies and threads rather 
happen within a CPU chip.
So I don't mind too much either way, but I think it's certainly ok to keep 
it in hw/s390x/ if you prefer that.

  Thomas