Disable Processor Counting based on Cgroups Container Support

[Bruno Borges]

Hi folks,

Looking at the source code, I couldn't identify a way (on tip, or any
previous release) to keep container support for memory limit, but disable
it for CPU limit.

While I could achieve this by not setting a CPU limit in my container
orchestration solution (e.g., Kubernetes), it wouldn't necessarily give me
what I am looking for: I do want to set a CPU limit at the container level,
but I want the JVM to count for all processors in the host/node. While I
can manually tweak this by modifying -XX:ActiveProcessorCount, this
requires me to know upfront how many processors the Node/Host will have.

Additionally, setting -XX:ActiveProcessorCount=-1 does not give me the
behavior I was expecting either.

The reason I raise this is due to the new In-place Pod Resource Resizing
feature in Kubernetes 1.27, that allows a pod to change the CPU limit
without restarting the pod. See this article for details:
https://medium.com/@karla.saur/trying-out-the-new-in-place-pod-resource-resizing-68a0b3c42b72

In an ideal world, the JVM would dynamically scale its thread pools, GC
threads, and other components at JVM and Application level accordingly, but
we are not there yet, I believe.

I'd love to hear what others think.

Thanks,
Bruno
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