$ python3.9 -m timeit -r 11 -s 'class A: pass' -s 'A.m = lambda s: None' -s 'a = A()' 'a.m; a.m; a.m; a.m; a.m'
1000000 loops, best of 11: 230 nsec per loop

$ python3.8 -m timeit -r 11 -s 'class A: pass' -s 'A.m = lambda s: None' -s 'a = A()' 'a.m; a.m; a.m; a.m; a.m'
2000000 loops, best of 11: 149 nsec per loop

$ python3.7 -m timeit -r 11 -s 'class A: pass' -s 'A.m = lambda s: None' -s 'a = A()' 'a.m; a.m; a.m; a.m; a.m'
2000000 loops, best of 11: 159 nsec per loop

$ python3.6 -m timeit -r 11 -s 'class A: pass' -s 'A.m = lambda s: None' -s 'a = A()' 'a.m; a.m; a.m; a.m; a.m'
10000000 loops, best of 11: 0.159 usec per loop

Timings made using the recent released python.org macOS 64-bit builds.

Probably bpo-37340

Is this regression is large enough to revive the free_list for bound methods?

This performance regression in still present in 3.9.0a6

Results from Tools/scripts/var_access_benchmark.py:

                     Python 3.8.2       Python 3.9.0a6
                     ------------       \--------------

read_boundmethod 27.7 ns 47.1 ns

Is this regression is large enough to revive the free_list
for bound methods?

Yes!

read_boundmethod 27.7 ns 47.1 ns

Extract of Tools/scripts/var_access_benchmark.py:

def read_boundmethod(trials=trials, a=A()):
    for t in trials:
        a.m;    a.m;    a.m;    a.m;    a.m
        a.m;    a.m;    a.m;    a.m;    a.m
        a.m;    a.m;    a.m;    a.m;    a.m
        a.m;    a.m;    a.m;    a.m;    a.m
        a.m;    a.m;    a.m;    a.m;    a.m

Which kind of code pattern is impacted by this performance regression, apart this micro-benchmark? Do you notice a significant slowdown in pyperformance?

When pyperformance was run before the change was merged, there was no significant difference:
https://bugs.python.org/issue37340#msg348425

In bpo-37340, you wrote that sorted(data, key=str.upper) is 70% slower. Would you mind to provide the benchmark?

I compared sorted(data, key=str.upper) performance between before the removal of the free list (parent of commit 3e54b57) and the current master branch, I get:

Mean +- std dev: [master] 167 us +- 4 us -> [cache] 179 us +- 7 us: 1.07x slower (+7%)

I cannot reproduce the "70% slowdown".

Raymond: How did you compile Python? What is your OS? How did you run your benchmark?

---

It's a quick & dirty benchmark run. I didn't use LTO+PGO and I didn't isolate my CPU. Maybe the difference of 12 ns is just caused by the noise of my coarse benchmark procedure.

I used commands:

# master
git checkout master
git clean -fdx
./configure && make && ./python -m venv env && env/bin/python -m pip install pyperf
env/bin/python -m pyperf timeit -s 'import random; data = [f"x{i}" for i in range(1000)]; random.shuffle(data)' 'sorted(data, key=str.upper)' -o ../master.json

# before removal of the free list
git checkout 3e54b57^
git clean -fdx
./configure && make && ./python -m venv env && env/bin/python -m pip install pyperf
env/bin/python -m pyperf timeit -s 'import random; data = [f"x{i}" for i in range(1000)]; random.shuffle(data)' 'sorted(data, key=str.upper)' -o ../master.json

That's a Fedora 31 using GCC -O3 (GCC 9.3.1).

--

The commit before the removal of the free list is:

commit 76b6451 (HEAD)
Date: Fri Jul 26 03:30:33 2019 +0200

Well, maybe I did a mistake.

By the way, in sorted(data, key=str.upper): str.upper is an unbound method, no?

$ ./python
Python 3.9.0a6+ (heads/master:d9a43e20fa, Apr 28 2020, 23:50:37) 
>>> type(str.upper)
<class 'method_descriptor'>