cpu_count is inconsistent between proc count and cpu count

[johnburnett]

cpu_count() seems to return inconsistent results between platforms. I think it comes down to an assumption on whether logical=False means "physical cpus" or "physical cores". On Windows, it looks like it returns the core count, while Linux returns the cpu count.

In my case, I was assuming the former (cores), and that's the actual useful value I'm needing (in this case, I want to run something on N-1 cores, leaving one full core for the user). However, on Linux, with a dual-proc X5550, I'm getting 2 for logical=False, and 16 for logical=True. Launching 15 threads swamps the machine, and 2 is obviously not great :). It works as expected on Windows (logical=False gives 8).

I have a patch for _pslinux.py:cpu_count_physical to make it behave the way I expected, but I wanted to check if all of the above sounds right? I also haven't looked at any other platform beyond Linux and Windows, and what is happening there.

[johnburnett]

Ping on this? (just got around to fixing the python 3 ci break related to this...)

[giovtorres]

Confirmed this PR fixes the same bug I found. The current cpu_count_physical() returns number of sockets, not number of physical cores.

[giampaolo]

I've just fixed this with a variant of your patch. Please confirm this works as expected.

[giovtorres]

Works. Thanks.