Re: [Xen-devel] PVH CPU hotplug design document

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 01/23/2017 05:35 AM, Jan Beulich wrote:
>>>> On 22.01.17 at 19:39, <boris.ostrovsky@xxxxxxxxxx> wrote:
>> On 01/18/2017 08:25 AM, Jan Beulich wrote:
>>>>>> On 18.01.17 at 12:54, <roger.pau@xxxxxxxxxx> wrote:
>>>> So, would it be fine to start a PVH Dom0 with as many vCPUs as what's 
>>>> returned
>>>> from dom0_max_vcpus, and mark them as enabled in the MADT. That's 
>>>> basically all
>>>> we need in order to match current PV Dom0 functionality?
>>> Yes, I think so.
>>
>> Have we then decided that we are not supporting ACPI hotplug for both 
>> dom0 and domU?
> I don't think anything has been decided yet, it's just that the road to
> (consistent) ACPI hotplug support still seems somewhat cloudy, so
> getting there (if we're convinced this is a worthwhile goal) may still
> take some time.


I am mostly interested in domU support at this point. This is the only
feature that I can think of right now that blocks domU support in Linux.

As I said in an earlier message I don't think dom0 needs ACPI hotplug
(or hotplug at all) while domU would benefit from it. But perhaps by
"consistent" you meant that you prefer both to behave in the same manner.

From Linux perspective one option could be to have domU with PV-style
vCPU on/offlining based on xenstore and switch to ACPI hotplug if/when
it becomes available. This, however, will need an indication from the
hypervisor. We could, for example, set ACPI_FADT_HW_REDUCED, as we
discussed earlier.

-boris



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