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float/cdecimal: significant slowdown in threaded pi benchmark compared to 3.9 #114922
Closed as not planned
Description
Bug description:
The following threaded pi benchmark runs faster on 3.9 than on main. The machine is a six-core i5-8600K with all cores saturated.
import time
import sys
import threading
import _decimal as C
import _pydecimal as P
def pi_float():
"""native float"""
lasts, t, s, n, na, d, da = 0, 3.0, 3, 1, 0, 0, 24
while s != lasts:
lasts = s
n, na = n+na, na+8
d, da = d+da, da+32
t = (t * n) / d
s += t
return s
def pi_cdecimal():
"""cdecimal"""
D = C.Decimal
lasts, t, s, n, na, d, da = D(0), D(3), D(3), D(1), D(0), D(0), D(24)
while s != lasts:
lasts = s
n, na = n+na, na+8
d, da = d+da, da+32
t = (t * n) / d
s += t
return s
def test_calc_pi():
C.getcontext().prec = 9
for func in [pi_float, pi_cdecimal]:
start = time.time()
for i in range(100000):
x = func()
print("%s:" % func.__name__.replace("pi_", ""))
print("result: %s" % str(x))
print("time: %fs\n" % (time.time()-start))
def test_threaded():
t = [0] * 6
for i in range(6):
t[i] = threading.Thread(target=test_calc_pi)
t[i].start()
for i in range(6):
t[i].join()
if __name__ == "__main__":
test_threaded()
3.9
===
float: [1.16, 2.15, 2.23, 2.80, 3.28, 4.36]
cdecimal: [2.89, 4.31, 3.02, 4.16, 4.45, 2.84]
real 0m9.365s
user 0m9.440s
sys 0m0.064s
main (--enable-gil)
===================
float: [5.301, 5.40, 6.03, 6.18, 7.19, 7.57]
cdecimal: [8.34, 6.88, 8.47, 8.49, 9.32, 7.21]
real 0m14.296s
user 0m14.472s
sys 0m0.164s
main (--disable-gil)
====================
float: [2.23, 2.90, 3.53, 4.15, 4.11, 4.19]
cdecimal: [6.68, 8.27, 7.42, 7.55, 9.72, 8.61]
real 0m12.250s
user 0m12.356s
sys 0m0.084s
CPython versions tested on:
3.9, CPython main branch
Operating systems tested on:
Linux
Activity
skrah commentedon Feb 2, 2024
See also: #114682 @rhettinger @mdickinson
skrah commentedon Feb 5, 2024
Notably, this issue is not present in @colesbury's
nogilrepository. Perhaps there is some interaction with other features that are being added at the same time.Observe that not only
_decimal(which currently has module state issues on main) is much faster, but also float.gpshead commentedon Mar 12, 2024
Procedural comment: For all involved on this issue, @skrah was banned from Python spaces per a Conduct Working Group recommendation to the Steering Council in 2020. A configuration oversight on our part in 2020 made that not so on Github. The intended ban of @skrah was reinstated on 2024-02-22. Our apologies to all for the consequences of this mixup (it was the first core dev ban done on our modern systems, we now understand how and why mistakes were made).
Stefan was informed of this privately via email and re-offered the opportunity to apologize for past actions and to accept our code of conduct going forwards per the original 2020 ban's terms and notification. We have not received a reply.
I'm posting this here as we view replying in the same forum where issues recently surfaced a reasonable way to notify past, present, and potential future participants of an incident response.
This says nothing for or against the validity of this issue. A new issue should be opened if people wish to proceed. I'm locking the comments on this one. For information on what the Github concept of a ban means, read the Github org ban docs.
-- The Python Steering Council, 2024 edition