PyPy vs CPython extension call overhead

c_extension_call_overhead.py

"""
Original code: https://gist.github.com/brentp/7e173302952b210aeaf3

Compare speed of a cython wrapper vs a cffi wrapper to the same underlying
C-code with a fast function and a longer-running function.
This should run anywhere that has cffi and cython installed.

    $ python3.6 -V
    Python 3.6.2 (default, Jul 17 2017, 16:44:45) 
    [GCC 4.2.1 Compatible Apple LLVM 8.1.0 (clang-802.0.42)] on darwin

    $ python3.6 compare_wrappers.py 
    adding 2 numbers with cffi wrapper: 0.299 usec
    adding 2 numbers with cython wrapper: 0.242 usec
    summing numbers inverses between 1 and 2000 with cffi wrapper: 6.356 usec
    summing numbers inverses between 1 and 2000 with cython wrapper: 6.312 usec    

    $ pypy3 -V
    Python 3.5.3 (3f6eaa010fce78cc7973bdc1dfdb95970f08fed2, Jan 13 2018, 18:14:01)
    [PyPy 5.10.1 with GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.39.2)]

    $ pypy3 compare_wrappers.py
    adding 2 numbers with cffi wrapper: 0.021 usec
    adding 2 numbers with cython wrapper: 2.789 usec
    summing numbers inverses between 1 and 2000 with cffi wrapper: 6.021 usec
    summing numbers inverses between 1 and 2000 with cython wrapper: 8.376 usec


It seems that

* In PyPy 5.10.1 cpyext (CPython API compatibility layers) has a constant overhead
    of ~2.5 usec per call.

* CFFI has zero overhead in PyPy (~20 nsec, comparable to plain C call).

* In CPython 3.6 CFFI and CPython C Extension API has almost identical overhead of
    ~250 nsec per call, with CFFI lagging a bit behind.
"""


from timeit import timeit
import cffi
import re
import os.path as op
import sys
import time



ffi = cffi.FFI()
ffi.cdef("""
int sum(int, int);
long inv_sum_between(int, int);
""")



# here is the C code that we are wrapping. One quick running function and
# another potentially long-running function.
code = """
int sum(int a, int b){
    return a + b;
}
long inv_sum_between(int a, int b){
   float sum = 0;    
   int i;
   for(i=a; i<=b; i++) sum += (1.0 / i);
   return (long)sum;
}
"""
C = ffi.verify(code)


import pyximport; pyximport.install()
with open('ccy.h', 'w') as fh:
    fh.write(code)

    # for cython, we also need to write the python callable wrappers.
cycode = """
cdef extern from "%s/ccy.h":
    int sum(int a, int b)
    long inv_sum_between(int a, int b)
cpdef int pysum(int a, int b):
    return sum(a, b)
cpdef long pyinv_sum_between(int a, int b):
    return inv_sum_between(a, b)
    """ % op.abspath(".")

with open('ccy.pyx', 'w') as fh:
    fh.write(cycode)


import ccy


start = time.time()
a = 0
for i in range(1000000):
    a = C.sum(a, a)
print("adding 2 numbers with cffi wrapper: {:.3f} usec".format(time.time() - start))

start = time.time()
a = 0
for i in range(1000000):
    a = ccy.pysum(a, a)
print("adding 2 numbers with cython wrapper: {:.3f} usec".format(time.time() - start))

start = time.time()
a = 0
for i in range(1000000):
    a = C.inv_sum_between(1, 2000 + a % 2)
print("summing numbers inverses between 1 and 2000 with cffi wrapper: {:.3f} usec"
        .format(time.time() - start))

start = time.time()
a = 0
for i in range(1000000):
    a = ccy.pyinv_sum_between(1, 2000 + a % 2)
print("summing numbers inverses between 1 and 2000 with cython wrapper: {:.3f} usec"
        .format(time.time() - start))