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[Python-Dev] Benchmarks why we need PEP 576/579/580

Jeroen Demeyer J.Demeyer at UGent.be
Sat Jul 21 12:21:12 EDT 2018 
Hello,

I finally managed to get some real-life benchmarks for why we need a 
faster C calling protocol (see PEPs 576, 579, 580).

I focused on the Cython compilation of SageMath. By default, a function 
in Cython is an instance of builtin_function_or_method (analogously, 
method_descriptor for a method), which has special optimizations in the 
CPython interpreter. But the option "binding=True" changes those to a 
custom class which is NOT optimized.

I ran the full SageMath testsuite several times without and with 
binding=True to find out any significant differences. The most dramatic 
difference is multiplication for generic matrices. More precisely, with 
the following command:

python -m timeit -s "from sage.all import MatrixSpace, GF; M = 
MatrixSpace(GF(9), 200).random_element()" "M * M"

With binding=False, I got
10 loops, best of 3: 692 msec per loop

With binding=True, I got
10 loops, best of 3: 1.16 sec per loop

This is a big regression which should be gone completely with PEP 580.

I should mention that this was done on Python 2.7.15 (SageMath is not 
yet ported to Python 3) but I see no reason why the conclusions 
shouldn't be valid for newer Python versions. I used SageMath 8.3.rc1 
and Cython 0.28.4.

I hope that this finally shows that the problems mentioned in PEP 579 
are real.


Jeroen.
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