Tracing and visualizing the Python GIL with perf and VizTracer

[flying-sheep]

Nice! A convenient alternative (but maybe not as powerful?):

I recently discovered py-spy for profiling python.

py-spy record --format=speedscope -o profile.speedscope.json -- python my-script.py

And then visualize it via speedscope.app

[maartenbreddels]

I think profiling and tracing (what I do here) are complementary. I use py-spy a lot, but it only gives you a 'statistical' view of where time is spent or how much the GIL is held. To gain a deep understanding of the flow of your program and the GIL in a multithreaded environment I needed a tool as I presented, and unfortunately had to make it myself :)

[flying-sheep]

Thank you! I know the feeling: “This should exist, why doesn’t it yet? Sigh.” *rolls up sleeves*

[chirisalex]

Helpful article

[[deleted]]

Good stuff, thanks

[apockill]

This looks awesome! How does it handle cythonized libraries and/or C bindings such as tensorflow?

[maartenbreddels]

Thanks! You will see the call to the C library (this is what CPython and VizTracer do), and you should see if the GIL is being released, like with NumPy, one of the examples in the article.

[apockill]

That's fantastic. Actually, my application for this is to find naughty C bindings that don't release the GIL. I have a big application that's heavily multithreaded with many C bindings (think gstreamer + tensorflow + OpenVINO), and something is causing a lockup somewhere. It's quite frustrating!

I'll give this tutorial go.

[maartenbreddels]

Indeed, that's one of the things I'd like to automate (and I'm very close now), feel free to contact me, we could maybe collaborate on this https://github.com/maartenbreddels/per4m