Hyper-V CPU details

[Neal Gompa]

On Thu, Oct 22, 2020 at 11:01 PM Matt Coleman <mcoleman at datto.com> wrote:
>
> Hello,
>
> I'm implementing domainGetVcpus and could use some guidance on what
> value to use for virVcpuInfo->cpu.
>
> Hyper-V does not allow the user to pin vCPUs to host CPUs and doesn't
> allow the user to see which host CPU a vCPU is currently running on.
> Since it's a type 1 hypervisor, none of its scheduling data is
> available to the Windows userspace: there aren't any processes or
> threads that correspond to vCPUs that I could query the OS scheduler
> about.
>
> My code currently sets it to -1, which produces the following `virsh
> vcpuinfo` output for a running VM with two cores:
>
> VCPU:           0
> CPU:            -1
> State:          running
> CPU time:       1684.5s
> CPU Affinity:   yyyy
>
> VCPU:           1
> CPU:            -1
> State:          running
> CPU time:       1346.0s
> CPU Affinity:   yyyy
>
> However, this doesn't match the comment in _virVcpuInfo's declaration,
> which says that -1 signifies an offline CPU:
>
> https://gitlab.com/libvirt/libvirt/-/blob/v6.8.0/include/libvirt/libvirt-domain.h#L1918
>
> Should I stick with -1? Or, should I introduce -2 as a value that
> indicates that the hypervisor doesn't provide that information? Or, is
> there some better way to handle this that I'm not aware of?
>

I would suggest introducing a new value. The problem with overloading
values is that if there's other code expecting that to mean something,
it gets confusing really quickly.


-- 
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