Re: [RFC PATCH 00/18] user-creatable cpu clusters

[Peter Maydell]

On Wed, 30 Mar 2022 at 13:56, Damien Hedde <damien.hedde@greensocs.com> wrote:
>
> Hi,
>
> This series add devices to be able to user-create (coldplug) cpu
> clusters. The existing cpu cluster dictates how cpus are exposed
> in gdb, but it does not handle the cpu objects creation. This series
> adds a new device to handle both issues and adds support for two
> architectures: arm and riscv.
>
> Please look at patches 2 and 3 for more details about the new device.
>
> Last part concerning the riscv is rfc as I do non-backward compatible
> updates. I'm not sure what migration (or other) constraints we have
> on these machines and I probably need to make some changes to cope
> with them.
>
> This series almost deprecates the cpu-cluster type as all uses
> but one are replaced.

I don't think we should have two different concepts which
are "a group of CPUs". It means we wind up with two different
ways to do something (which we have too many examples of
already), only one of which gets to use the nicer, more obvious
name.

The stated motivation is to allow user creation of CPU clusters,
but I'm not sure how this would work -- CPUs need a lot of
things wiring up like interrupt lines and memory regions, which
you can't do on the command line anyway. Do you have an example
of what the new code lets you do?

thanks
-- PMM