Bug report

Bug description:

While working on the free-threaded GC, I noticed this performance regression with the default build GC. Running the attached script (bm_gc_collect.py) with the main branch of Python shows much worse performance vs 3.13. I get 20.8 seconds for the main branch and 3.3 seconds for 3.13. Adding gc.disable() before calling benchmark_collection() seems to fix it.

bm_gc_collect.py.txt

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-129210: GC optimisations for case where no objects being collected have finalizers #132488