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giampaolo / psutil

Cross-platform lib for process and system monitoring in Python
BSD 3-Clause "New" or "Revised" License
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[macOS] CPU utilization contains zeroes #2368

Open ArneTR opened 5 months ago

ArneTR commented 5 months ago

Summary

Description

I searched for utilization and could not find anything that matches this, so I hope it is not a dup.

When using psutil.cpu_percent(0.1) on my macOS while running a constant stress in parallel (stress-ng -c 1) I get a lot of zeros in between.

Screenshot 2024-02-05 at 10 38 33 AM

The same behaviour is also when I increase the stress to more cores. Say 8

>>> while True: psutil.cpu_percent(0.1)
...
100.0
100.0
100.0
100.0
0.0
0.0
0.0
0.0
0.0

The same behaviour does not happen on linux machines.

giampaolo commented 3 months ago

What does htop or similar tools show? 0.1 is a small interval. Task manager tools usually use 1 sec instead. What happens if you use 1 sec?

ArneTR commented 3 months ago

htop works fine. You can just let it run with 100ms resolution and the many consecutive "0" values do not occur.

For clarification: These values do occuer always no matter what kind of load we are running. So even if all cores are fully stressed zeros creep in, which is probably due to the used syscall.

We have actually created working code for one our tools. Please find it here: https://github.com/green-coding-solutions/green-metrics-tool/blob/main/metric_providers/cpu/utilization/mach/system/source.c

We are using host_processor_info and not host_statistics.

See also discussion here: https://github.com/green-coding-solutions/green-metrics-tool/issues/330

ArneTR commented 3 months ago

@ribalba FYI

ribalba commented 3 months ago

I wrote a blog article about the problem here:

https://www.green-coding.io/blog/cpu-utilization-mac/

giampaolo commented 3 months ago

Nice finding! It's kind of shocking that CPU metrics on macOS have been wrong for so long and nobody noticed.

ArneTR commented 3 months ago

To be fair, it is unknown exactly in which version of macOS this isse happens and if it also is on all chip.s

@ribalba and I both have M1 machines. Untested on Intel and M2.

We are happy to provide a PR and some tests for macOS that test this feature (Stressing a core and seeing if zeros still exist in output), but I see that this repo currently has no macOS Github Actions runner defined.

If we provide a PR, does this repo have the possiblity to have a macOS Runner running that can test the CPU Utilization?

giampaolo commented 3 months ago

We currently have CI runners for macOS x86-64 and arm (this one was added yesterday).