RFR: 8339148: Add os::active_physical_processor_count() API

[David Holmes]

On Thu, 29 Aug 2024 12:38:40 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

> Please review this rather trivial patch for adding `os::active_physical_processor_count()` function. It is useful to have that info on Linux for the container code which bounds the CPU limit above by that value. Also, the old `os::Linux::active_processor_count()` was protected and had a bit of a misleading name. As a bonus, we can get rid of some `friend class` smells.
> 
> **Testing**:
> - [x] GHA
> - [x] Container tests and cgroup gtests on linux x86_64
> 
> Thoughts?

I'm not clear exactly what you need here but "physical" is not what you are looking up.

src/hotspot/os/linux/os_linux.cpp line 4833:

> 4831: 
> 4832: // Return the active CPUs irrespective of the system being containerized
> 4833: // or not. Thus, this returns the host active cpus in a container.

No it doesn't! The comment for the function you call states clearly:

// Get the current number of available processors for this process.

This is not related to "physical count" at all!

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Changes requested by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20768#pullrequestreview-2270580489
PR Review Comment: https://git.openjdk.org/jdk/pull/20768#discussion_r1737466694