New issue 2401: complex number calculations much slower on windows than on
linux/osx?
https://bitbucket.org/pypy/pypy/issues/2401/complex-number-calculations-much-slower-on
Irmen de Jong:
(copied from message posted to comp.lang.python)
I've stumbled across a peculiar performance issue with Pypy across some
different
platforms. It was very visible in some calculation heavy code that I wrote that
uses
Python's complex number type to calculate the well-known Mandelbrot set.
Pypy running the code on my Windows machine is doing okay, but when running the
same
code on Pypy on different systems, the performance difference is so big it is
not even
funny. The other implementations are MUCH faster than the windows one. Which is
quite
unexpected because the other machines I've tested on have the same or much lower
physical CPU specs than the windows machine. Here's the comparison:
Machine specs:
* Windows: 64 bits Windows 7, Intel Core 2 Quad 3.4 Ghz
* Linux: 32 bits Mint 18, Virtualbox VM on above windows machine
* Mac mini: OS X 10.11.6, Intel Core 2 Duo 2.53 Ghz
The 'iterations' function mentioned below is looking like this:
```python
def iterate():
print("iterating...")
z = .1+.1j
c = z
for _ in range(12345678):
z = z*z + c
z = z*z + c
z = z*z + c
z = z*z + c
z = z*z + c
z = z*z + c
if abs(z) > 2:
raise ValueError("should not go towards infinity")
print(abs(z))
```
Rest of the test code I've been using is here:
https://gist.github.com/irmen/c6b12b4cf88a6a4fcf5ff721c7089078
Test results:
```
#!
function: mandel / iterations
Mac mini, Pypy 5.4.1 (64-bit): 0.81 sec / 0.65 sec
Linux, Pypy 5.1 (32-bit): 1.06 sec / 0.64 sec
Windows, Pypy 5.4.1 (32-bit): 5.59 sec / 2.87 sec
```
What could cause such a huge difference?
Is it perhaps a compiler issue (where gcc/clang are MUCH better at optimizing
certain
things, although I wonder how much of a factor this is because Pypy is doing
JITting by
itself as far as I am aware)? Or is something strange going on with the way
the
complex number type is implemented? (the difference doesn't occur when using
only floats)
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