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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] psutil.Process(pid).cpu_percent calculation result is inaccurate #2411

Open RLYRLY opened 5 months ago

RLYRLY commented 5 months ago

Summary

proc = psutil.Process(pid) cpu_usage = proc.cpu_percent(interval=1) print(f"Process '{proc.name()}' (PID: {proc.pid}) CPU utilization: {cpu_usage}%") image psutil:0.1%

giampaolo commented 5 months ago

How are you comparing the 2? If you want to compare with top/htop you should do it in a loop, like this:

p = psutil.Process(PID)
while 1:
    print(p.cpu_percent(interval=None)
    time.sleep(1)
RLYRLY commented 5 months ago

@giampaolo First of all, thank you for your help. I used loops for benchmarking and there is no change. Under arm64, the cpu utilization of the psutil calculation process is very different from that of htop calculation. In addition, I use other mac (inter chips), and the calculation results are basically the same as htop.

RLYRLY commented 5 months ago

@giampaolo Hello, please help me answer this question if you have time, it is very important to me.

giampaolo commented 5 months ago

Sorry but I have no idea. I don't have the hardware to test this against. Perhaps on arm64 process CPU metrics work differently and require using a different API. It would not be a first on macOS.

RLYRLY commented 5 months ago

@giampaolo Understood, thank you, if there is any progress in the future, please try to synchronize it. Let me investigate the specific reasons here.

zhang25121 commented 4 months ago

I ran into the same problem on a 32 core window machine, and I found that on powerful machines, the CPU cores didn't always work

dbwiddis commented 1 month ago

I suspect the issue is a conversion based on the clock frequency somewhere.

x64 uses 1 tick per millisecond. aarch64 uses 3 ticks per 125 milliseconds. You can find the conversion in the timebase_frequency field of any CPU in the IORegistry.

Here's a Java/JNA-based calculation of the offset: https://github.com/oshi/oshi/blob/099a4a1153effdfe4547c25052d2df4961e4d7eb/oshi-core/src/main/java/oshi/software/os/mac/MacOSProcess.java#L62-L88

If you multiply the psutil value by 41.6666... (125/3) do you get the expected result?

See also my answer at https://stackoverflow.com/a/76151406/1161484 with more detail including (untested) C code that might be appropriate here.

dbwiddis commented 1 month ago

As a follow-up, I see the existing code uses the CLK_TCK constant for division, which apparently doesn't work on arm64. The linked SO post in my previous comment also includes a few other native command calls available on arm64 mac which might be able to be used at compile time rather than my Java run-time hack.

In any case, I'm pretty sure the answer is as simple as "on Apple Silicon, multiply by 125/3" and finding the right way to define that in the code is something I'll leave to the C experts.

See also same bug/fix on my Java-based repo: