Python 2.7.8 (64bit) on Windows (64bit) is half as fast as 2.7.8 (64bit) on Ubuntu (64bit)

Question

On Linux it takes 1.09171080828 secs.

On Windows it takes 2.14042000294 secs.

Code for the benchmark:

import time


def mk_array(num):
        return  [x for x in xrange(1,num)]

def run():
        arr = mk_array(10000000)
        x = 0
        start = time.time()
        x = reduce(lambda x,y: x + y, arr)
        done = time.time()
        elapsed = done - start
        return elapsed

if __name__ == '__main__':
        times = [run() for x in xrange(0,100)]
        avg = sum(times)/len(times)
        print (avg)

I am aware that the GIL creates more or less single threaded scripts.

Windows box is my Hyper-V host but should be beefy enough to run a single threaded script at full bore. 12-cores 2.93Ghz Intel X5670s, 72GB ram, etc.

Ubuntu VM has 4-cores and 8GB of ram.

Both are running Python 2.7.8 64-bit.

Why is windows half as fast?

edit: I've lopped two zeros and linux finishes in 0.010593495369 seconds, and windows in 0.171899962425 seconds. Thanks everyone, curiosity satisfied.

Answer 1

It is because of the size of the long in windows, in windows a long is 32 bits in unix it is 64 bits so you are hitting Arbitrary-precision_arithmetic issues sooner which are costlier to allocate.

Related question Why are python's for loops so non-linear for large inputs

If you benchmark the xrange alone you will see a considerable difference.

The reasoning behind windows use of LLP64 seems to be compatibility with 32-bit code:

Another alternative is the LLP64 model, which maintains compatibility with 32-bit code by leaving both int and long as 32-bit. "LL" refers to the "long long integer" type, which is at least 64 bits on all platforms, including 32-bit environments.

Taken from wiki/64-bit_computing