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os.process_cpu_count(): get the number CPUs usable by the current process #109649
Description
Feature or enhancement
os.cpu_count() returns the total number of CPUs that the current machine has. On Unix, sched_setaffinity() can reduce the number of CPU "usable" by a process. Currently, os.cpu_count() docstring contains a recipe how to get the number of usable CPUs:
>>> import os; help(os.cpu_count)
cpu_count()
Return the number of CPUs in the system; return None if indeterminable.
This number is not equivalent to the number of CPUs the current process can
use. The number of usable CPUs can be obtained with
``len(os.sched_getaffinity(0))``
I propose to add an affinity optional keyword-only parameter to os.cpu_count() which would return len(os.sched_getaffinity(0)).st
UPDATE: Rename usable parameter to affinity.
Linked PRs
- gh-109649: Add affinity parameter to os.cpu_count() #109652
- gh-109649: Add os.process_cpu_count() function #109907
- gh-109649: Use os.process_cpu_count() #110165
- [3.12] gh-109649: Enhance os.cpu_count() documentation #110169
- [3.11] [3.12] gh-109649: Enhance os.cpu_count() documentation (GH-110169) #110226
- gh-109649: Fix test_os.test_process_cpu_count_affinity() #111689
Activity
vstinner commentedon Sep 21, 2023
os.cpu_count() issues (open and closed):
Previously, the function was known as multiprocessing.cpu_count():
pythongh-109649: Add usable parameter to os.cpu_count()
pythongh-109649: Add usable parameter to os.cpu_count()
pythongh-109649: Add usable parameter to os.cpu_count()
vstinner commentedon Sep 21, 2023
On Windows, maybe it can be implemented with GetProcessGroupAffinity(), GetProcessAffinityMask(), GetActiveProcessorGroupCount() and GetActiveProcessorCount().
GetProcessGroupAffinity():
https://learn.microsoft.com/en-us/windows/win32/api/processtopologyapi/nf-processtopologyapi-getprocessgroupaffinity
vstinner commentedon Sep 21, 2023
On Windows, a CPU affinity can be run with
start /affinitycommand. Example to only run Python on the firstCPU:pythongh-109649: Add affinity parameter to os.cpu_count()
[-]os.cpu_count(): add "usable" parameter to get the number of "usable" CPUs[/-][+]os.cpu_count(): add "affinity" parameter to get the number of logical CPUs usable by the current process[/+]pythongh-109649: Add affinity parameter to os.cpu_count()
pythongh-109649: Add affinity parameter to os.cpu_count()
pythongh-109649: Add affinity parameter to os.cpu_count()
pythongh-109649: Add os.process_cpu_count() function
pythongh-109649: Add os.process_cpu_count() function
pythongh-109649: Add os.process_cpu_count() function
5 remaining items
pythongh-109649: Use os.process_cpu_count()
pythongh-109649: Use os.process_cpu_count()
pythongh-109649: Use os.process_cpu_count()
pythongh-109649: Enhance os.cpu_count() documentation
pythongh-109649: Enhance os.cpu_count() documentation
gh-109649: Use os.process_cpu_count() (#110165)
[3.12] gh-109649: Enhance os.cpu_count() documentation (#110169)
[3.12] pythongh-109649: Enhance os.cpu_count() documentation (pythonG…
[3.11] [3.12] gh-109649: Enhance os.cpu_count() documentation (GH-110169
pythongh-109649: Fix test_os.test_process_cpu_count_affinity()
gh-109649: Fix test_os.test_process_cpu_count_affinity() (#111689)
pythongh-109649: Fix test_os.test_process_cpu_count_affinity() (pytho…
pythongh-109649: Add os.process_cpu_count() function (python#109907)
pythongh-109649: Use os.process_cpu_count() (python#110165)
pythongh-109649: Fix test_os.test_process_cpu_count_affinity() (pytho…