Re: [PATCH v8 08/12] s390x/cpu_topology: implementing numa for the s390x topology

[Janis Schoetterl-Glausch]

On 6/20/22 16:03, Pierre Morel wrote:
> S390x CPU Topology allows a non uniform repartition of the CPU
> inside the topology containers, sockets, books and drawers.
> 
> We use numa to place the CPU inside the right topology container
> and report the non uniform topology to the guest.
> 
> Note that s390x needs CPU0 to belong to the topology and consequently
> all topology must include CPU0.
> 
> We accept a partial QEMU numa definition, in that case undefined CPUs
> are added to free slots in the topology starting with slot 0 and going
> up.

I don't understand why doing it this way, via numa, makes sense for us.
We report the topology to the guest via STSI, which tells the guest
what the topology "tree" looks like. We don't report any numa distances to the 
guest.
The natural way to specify where a cpu is added to the vm, seems to me to be
by specify the socket, book, ... IDs when doing a device_add or via -device on 
the command line.

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