Allow reporting cpu physical core count.

[andrewd-zededa]

cpu.Info() reports a list of cpus and the list
will be double in length when hyperthreading
is enabled. This difference also scales cpu utilization.

New config property: cpu.stats.physicalcore.enabled
Default set to false to allow opt-in usage.
When set to true domainmgr will:
Take the last cpu.InfoStat's CoreID
Add 1 (since CoreID starts at 0)
Set HostMemory.Ncpus to that value.

[OhmSpectator]

I need to review this PR in more detail. As far as I remember, Core IDs are not always continuous in modern CPUs. Also, I want to understand if it affects the CPU allocator logic (part of CPU pinning).

[eriknordmark]

Note that this will affect the reported scaled CPU usage. Is that the intent? As opposed to reporting cores instead or hyperthreads as the CPUs shows in the UI.

That means that with hyperthreading the UI can calculate a CPU usage which exceeds 100% (if reportPhyCores is set).

[andrewd-zededa]

@eriknordmark yeah the intent for this PR is to scale cpu utilization differently. The use case is an eve node which may have 4 physical cores and has hyperthreading enabled leading to 8 threads. A vm app is deployed with 2 cpus and the vm running some cpu stress utility like "stress-ng --cpu 2". In this case the vm will see 100% cpu utilization and in existing cpu accounting the utilization is scaled by 8 threads and top level eve node cpu utilization reports 25% utilization. With this config property enabled the utilization would instead be scaled by 4 cores and report 50% utilization.

This PR is not linked to the existing kubevirt PRs.

@OhmSpectator I started with an alternate option which did a simple scan through the list to find the highest CoreId. I removed that to hopefully skip a loop, it could certainly be reimplemented.

[eriknordmark]

@eriknordmark yeah the intent for this PR is to scale cpu utilization differently. The use case is an eve node which may have 4 physical cores and has hyperthreading enabled leading to 8 threads. A vm app is deployed with 2 cpus and the vm running some cpu stress utility like "stress-ng --cpu 2". In this case the vm will see 100% cpu utilization and in existing cpu accounting the utilization is scaled by 8 threads and top level eve node cpu utilization reports 25% utilization. With this config property enabled the utilization would instead be scaled by 4 cores and report 50% utilization.

But if everything is busy including the hyperthreads, then it will might report up to 200% CPU usage for the edge node. Isn't that going to be confusing?
Note that users who don't care about hyperthreading can disable it in the BIOS AFAIK.