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Late follow-up after a discussion with Jens about a different document pointed out that my answer was ambiguous and easy to misinterpret.

> On 7 Jul 2021, at 22:46, Jens Freimann <jfreiman at redhat.com> wrote:
> 
> On Wed, Jul 7, 2021 at 12:48 PM Christophe de Dinechin
> <dinechin at redhat.com> wrote:
>> On 2021-07-07 at 01:31 UTC, "Adams, Eric" <eric.adams at intel.com> wrote...
>>> Christophe,
>>> 2) I also observed that Pod Overhead isn't used in the calculation for
>>> hotplugged CPU's.
>> 
>> That seems correct. The pod overhead accounts for the overhead "outside" the
>> VM, i.e. virtiofsd, qemu's own memory needs, the extra cost of doing I/Os,
>> etc. So this is additional resources the host needs, not the VM.

That wording be interpreted as the pod overhead _only_ accounting for overhead outside the VM. That is not what I intended. I intended to point out that it _also_ accounts for overhead outside the VM. In other words, it is the sum of how much memory the VM needs just to get started (e.g. 110M for a basic kernel, 300M for a more standard RHEL-style kernel), which includes the memory used by the agent, and of additional processes outside the VM, like virtiofsd, the shim, etc.


> 
> This is very counter-intuitive and also doesn't fit the 'Motivation'
> section in the original
> design[1]. Wouldn't this lead to wrong results for the resource quota
> and scheduler calculations?
> 
> [1] https://github.com/kubernetes/enhancements/tree/master/keps/sig-node/688-pod-overhead
> 
> regards
> Jens
>