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

[Claudio Fontana <cfontana@suse.de>]

On 3/14/24 17:44, Nina Schoetterl-Glausch wrote:
> 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.
> 
> [...]
>>
> 

Thank you for your responses Thomas and Nina,
I have just sent a patch that tries to make it even more explicit.

"[PATCH] docs/s390: clarify even more that cpu-topology is KVM-only"

Thanks,

Claudio