Re: [Qemu-devel] should KVM or userspace be the one which decides what MIPIDR/affinity values to assign to vcpus?

[Peter Maydell]

On 9 June 2015 at 13:27, Marc Zyngier <address@hidden> wrote:
> On 09/06/15 12:24, Peter Maydell wrote:
>> So either:
>>  * QEMU needs to tell the kernel the MPIDR for each vCPU
>>  * QEMU needs to ask the kernel the MPIDR for each vCPU
>>
>> Which is better? The latter is simpler and will work with
>> existing kernels. The former would let us (for instance)
>> use KVM when we're modelling (real world) boards which have
>> particular cluster configurations (which might not match the
>> kernel's current simplistic "always 16 CPUs at Aff0" setup).
>
> Given that it is userspace that provides the description of the
> platform, it feels natural to let userspace set MPIDR accordingly.
>
> This will require some interesting rework in the kernel, but this
> doesn't feel too bad.

On the other hand QEMU needs to keep working with current kernels,
so we need the "ask the kernel" code at least for the moment.
Probably needs a capability for "kernel allows userspace to
set MPIDR" so we can adapt.

-- PMM