BSON performance regression in Python 3.12

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    • Type: Bug
    • Resolution: Won't Do
    • Priority: Major - P3
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      There seems to be a BSON performance regression in Python 3.12. Discovered because PYTHON-5203 just upgraded our perf benchmarks from Python 3.10 to 3.13 and multiple BSON benchmarks dropped by 40%:
      https://spruce.mongodb.com/task/mongo_python_driver_perf_tests_perf_8.0_standalone_e6e8650cc95314e742a30244b5db0239f5259f68_25_03_13_19_08_41/trend-charts?execution=0&sortBy=STATUS&sortDir=ASC

      I can reproduce a regression in Python 3.12 and Python3.13 locally as well. Here's 3.10:

      platform darwin -- Python 3.10.11, pytest-8.3.5, pluggy-1.5.0 -- /Users/shane/work/pycharm/pymongo-py310/bin/python
...
test/performance/perf_test.py::TestFlatEncoding::runTest Completed TestFlatEncoding 660.347 MB/s, MEDIAN=0.009s, total time=0.100s, iterations=10

      3.11:

      platform darwin -- Python 3.11.4, pytest-8.3.4, pluggy-1.5.0 -- /Users/shane/work/pycharm/pymongo-py311/bin/python
...
test/performance/perf_test.py::TestFlatEncoding::runTest Completed TestFlatEncoding 657.964 MB/s, MEDIAN=0.009s, total time=0.101s, iterations=10

      3.12:

      platform darwin -- Python 3.12.4, pytest-8.3.3, pluggy-1.5.0 -- /Users/shane/work/pycharm/pymongo-py312/bin/python
...
test/performance/perf_test.py::TestFlatEncoding::runTest Completed TestFlatEncoding 489.287 MB/s, MEDIAN=0.012s, total time=0.110s, iterations=8

      3.13:

      platform darwin -- Python 3.13.0, pytest-8.3.4, pluggy-1.5.0 -- /Users/shane/work/pycharm/pymongo-3.13/bin/python
...
test/performance/perf_test.py::TestFlatEncoding::runTest Completed TestFlatEncoding 516.190 MB/s, MEDIAN=0.012s, total time=0.106s, iterations=8

            Assignee:
            Noah Stapp
            Reporter:
            Shane Harvey
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              Created:
              Updated:
              Resolved: