我正在尝试评估一些方法,并且我遇到了性能绊脚石。使用Cython优化简单的CPU绑定循环并替换列表
为什么我的cython代码太慢?我的期望是代码运行速度要快很多(对于只有256 ** 2条目的2d循环,也许是纳秒),而不是毫秒。
这里是我的测试结果:
$ python setup.py build_ext --inplace; python test.py
running build_ext
counter: 0.00236220359802 sec
pycounter: 0.00323309898376 sec
percentage: 73.1 %
我最初的代码看起来是这样的:
#!/usr/bin/env python
# encoding: utf-8
# filename: loop_testing.py
def generate_coords(dim, length):
"""Generates a list of coordinates from dimensions and size
provided.
Parameters:
dim -- dimension
length -- size of each dimension
Returns:
A list of coordinates based on dim and length
"""
values = []
if dim == 2:
for x in xrange(length):
for y in xrange(length):
values.append((x, y))
if dim == 3:
for x in xrange(length):
for y in xrange(length):
for z in xrange(length):
values.append((x, y, z))
return values
这适用于我所需要的,但速度很慢。对于给定的暗淡,长度=(2,256),我看到iPython的时间约为2.3ms。
为了加快速度,我开发了一个cython等价物(我认为它是等价的)。
#!/usr/bin/env python
# encoding: utf-8
# filename: loop_testing.pyx
# cython: boundscheck=False
# cython: wraparound=False
cimport cython
from cython.parallel cimport prange
import numpy as np
cimport numpy as np
ctypedef int DTYPE
# 2D point updater
cpdef inline void _counter_2d(DTYPE[:, :] narr, int val) nogil:
cdef:
DTYPE count = 0
DTYPE index = 0
DTYPE x, y
for x in range(val):
for y in range(val):
narr[index][0] = x
narr[index][1] = y
index += 1
cpdef DTYPE[:, :] counter(dim=2, val=256):
narr = np.zeros((val**dim, dim), dtype=np.dtype('i4'))
_counter_2d(narr, val)
return narr
def pycounter(dim=2, val=256):
vals = []
for x in xrange(val):
for y in xrange(val):
vals.append((x, y))
return vals
和定时的调用:
#!/usr/bin/env python
# filename: test.py
"""
Usage:
test.py [options]
test.py [options] <val>
test.py [options] <dim> <val>
Options:
-h --help This Message
-n Number of loops [default: 10]
"""
if __name__ == "__main__":
from docopt import docopt
from timeit import Timer
args = docopt(__doc__)
dim = args.get("<dim>") or 2
val = args.get("<val>") or 256
n = args.get("-n") or 10
dim = int(dim)
val = int(val)
n = int(n)
tests = ['counter', 'pycounter']
timing = {}
for test in tests:
code = "{}(dim=dim, val=val)".format(test)
variables = "dim, val = ({}, {})".format(dim, val)
setup = "from loop_testing import {}; {}".format(test, variables)
t = Timer(code, setup=setup)
timing[test] = t.timeit(n)/n
for test, val in timing.iteritems():
print "{:>20}: {} sec".format(test, val)
print "{:>20}: {:>.3} %".format("percentage", timing['counter']/timing['pycounter'] * 100)
而对于参考,setup.py构建用Cython代码:
from distutils.core import setup
from Cython.Build import cythonize
import numpy
include_path = [numpy.get_include()]
setup(
name="looping",
ext_modules=cythonize('loop_testing.pyx'), # accepts a glob pattern
include_dirs=include_path,
)
编辑: 链接到工作版本:https://github.com/brianbruggeman/cython_experimentation
你的cython代码非常好。如果使用'narr [index] [0] = x'实际上并没有执行赋值操作(并且执行缓慢的C python API调用),请使用'narr [index,0] = x'(对于纯numpy同样如此)。另外,尝试在你的'setup.py'中设置'extra_compile_args = ['-O3','-march = native']'和'extra_link_args = [' - O3','-march = native']'这应该会加快速度向上。 – rth
谢谢!我会试试这个。 –
@rth'narr [index,0]'明确地解决了这个问题。我现在的速度大概是100倍。我没有看到多余的编译/链接选项的变化。但是,我不介意在这一点上留下这些内容。万分感谢!您想添加答案吗? –