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gh-109649: Fix test_os.test_process_cpu_count_affinity() #111689

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merged 1 commit into from
Nov 3, 2023

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@vstinner vstinner commented Nov 3, 2023

When CPUs are isolated on Linux, os.process_cpu_count() is smaller than os.cpu_count(). Fix the test for this case.

Example with "isolcpus=5,11 rcu_nocbs=5,11" options passed to a Linux command line to isolated two logical CPUs:

$ ./python -c 'import os; print(os.process_cpu_count(), "/", os.cpu_count())'
10 / 12

When CPUs are isolated on Linux, os.process_cpu_count() is smaller
than os.cpu_count(). Fix the test for this case.

Example with "isolcpus=5,11 rcu_nocbs=5,11" options passed to a Linux
command line to isolated two logical CPUs:

$ ./python -c 'import os; print(os.process_cpu_count(), "/", os.cpu_count())'
10 / 12
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vstinner commented Nov 3, 2023

@corona10 @gpshead: Do you think that it would be worth it to document this special case in os.process_cpu_count()?

"On Linux, if some CPUs are isolated, os.process_cpu_count() reports less usable CPUs than os.cpu_count()."

Or is it a known fact?

I'm asking if we should "advertize" more this function to users this way ;-)

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gpshead commented Nov 3, 2023

: Do you think that it would be worth it to document this special case in os.process_cpu_count()?

"On Linux, if some CPUs are isolated, os.process_cpu_count() reports less usable CPUs than os.cpu_count()."

Or is it a known fact?

I think we can consider this "known" in the sense that the number of possible ways for this to be true on a system is more than we can accurately enumerate in our docs.

@vstinner vstinner enabled auto-merge (squash) November 3, 2023 17:27
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vstinner commented Nov 3, 2023

Ok, thanks for the review @gpshead.

@vstinner vstinner merged commit 244e37b into python:main Nov 3, 2023
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@vstinner vstinner deleted the process_cpu_count branch November 3, 2023 23:53
aisk pushed a commit to aisk/cpython that referenced this pull request Feb 11, 2024
…n#111689)

When CPUs are isolated on Linux, os.process_cpu_count() is smaller
than os.cpu_count(). Fix the test for this case.

Example with "isolcpus=5,11 rcu_nocbs=5,11" options passed to a Linux
command line to isolated two logical CPUs:

$ ./python -c 'import os; print(os.process_cpu_count(), "/", os.cpu_count())'
10 / 12
Glyphack pushed a commit to Glyphack/cpython that referenced this pull request Sep 2, 2024
…n#111689)

When CPUs are isolated on Linux, os.process_cpu_count() is smaller
than os.cpu_count(). Fix the test for this case.

Example with "isolcpus=5,11 rcu_nocbs=5,11" options passed to a Linux
command line to isolated two logical CPUs:

$ ./python -c 'import os; print(os.process_cpu_count(), "/", os.cpu_count())'
10 / 12
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