Performance regression 6.6.3.1 -> 6.7.0

When upgrading from PySide 6.6.3.1 to 6.7.0 (both from PyPi), I get a huge performance regression in my application (https://github.com/SanderVocke/shoopdaloop), making it borderline unusable.

The application in question has a mix of Python and QML, including using Python objects as registered QML types.

During application startup and dynamic object creations, a slowdown of about 5x can be seen.

I am having trouble providing any kind of meaningful information as to where the performance slowdown is coming from. I am hoping you can help me with some suggestions on how to further root cause this.

What I have tried:

• QML debugging traces in QtCreator. This shows that basically the entire application start-up is multiple times slower. More or less every object created is slowed down w.r.t. 6.6.3.1 (as opposed to one particular action only costing more time).
• Sample-based profiling with perf. Comparing the two pyside versions, in 6.7.0 there are large chunks of time going to functions in libshiboken, which are not significantly visible in 6.6.3.1.
  • I don't have debug symbols so I cannot see which function(s) in shiboken are the culprit here.
  • Building pyside6 from source using the setup.py script with --debug did not yield a working PySide in my case. Trying to start with this self-built version gives an infinite recursion error in importlib. I am not sure how to proceed.
• Tried creating a minimal QML example which instantiates objects with createObject() in a loop and times the result. For these minimal examples, performance was always comparable between the two PySide versions, also when adding some bindings and a Python registered object into the mix.
• Force all objects I create with incubateObject() to finish immediately using forceCompletion(), to rule out that this somehow comes from the incubator implementation. I see the same performance difference.

I realize that this is very vague. I am hoping someone has a hint as to how I can investigate this myself to get some more concrete information. Is there a debug version of pyside6 that I can grab from anywhere - or even on a container image? Any pointers on how to get pyside6 built with debug symbols reliably?

I can provide/upload if of any help:

• QML debug traces
• perf data
• Python wheel of the application in question, which can be run both with v6.7.0 and v6.6.3.1

Thanks in any case.