Context

Investigate apparent minor perf regression in SSL benchmarks due to PYTHON-3175:

I suspect the issue is caused by the extra overhead of calling wait_for_read().

In the PR for PYTHON-3175 I noted this change https://github.com/mongodb/mongo-python-driver/pull/1465#issuecomment-1896673108:

Looking at the perf results it does appear this results in a ~5% decrease. Locally with 100 threads I see a decrease of somewhere between 5-10%:

$ git:(master) time python bench-100-threads.py 
python bench-100-threads.py  6.61s user 8.06s system 129% cpu 11.320 total
$ git:(master) time python bench-100-threads.py 
python bench-100-threads.py  6.65s user 8.13s system 130% cpu 11.297 total
$ git:(master) time python bench-100-threads.py 
python bench-100-threads.py  6.86s user 8.52s system 129% cpu 11.842 total

vs

$ git:(NoahStapp-PYTHON-3175) time python bench-100-threads.py 
python bench-100-threads.py  7.18s user 8.52s system 127% cpu 12.323 total
$ git:(NoahStapp-PYTHON-3175) time python bench-100-threads.py 
python bench-100-threads.py  7.26s user 8.88s system 130% cpu 12.320 total
$ git:(NoahStapp-PYTHON-3175) time python bench-100-threads.py 
python bench-100-threads.py  7.34s user 9.02s system 132% cpu 12.335 total

With a single threaded benchmark the total execution time is about the same but the user and system CPU time goes up by 5%:

$ git:(master) time python bench-single-thread.py
1.80s user 0.34s system 50% cpu 4.259 total
$ git:(master) time python bench-single-thread.py
1.81s user 0.34s system 50% cpu 4.267 total
$ git:(master) time python bench-single-thread.py
1.85s user 0.36s system 51% cpu 4.277 total

VS

$ git:(NoahStapp-PYTHON-3175) time python bench-single-thread.py
1.99s user 0.41s system 56% cpu 4.277 total
$ git:(NoahStapp-PYTHON-3175) time python bench-single-thread.py
1.97s user 0.42s system 56% cpu 4.239 total
$ git:(NoahStapp-PYTHON-3175) time python bench-single-thread.py
1.97s user 0.41s system 55% cpu 4.254 total

Here's the single-threaded benchmark:

from pymongo import MongoClient
client = MongoClient()
N_ITERATIONS = 50000

def main():
    for _ in range(N_ITERATIONS):
        client.admin.command('ping')

if __name__ == "__main__":
    main()

Definition of done

Remove regressions on all benchmarks when compared to 4.6.2.

Pitfalls

Note that some benchmarks have high run to run variance which makes it a little harder to spot true regressions.