Building CPython

[MRAB]

On 2015-05-14 22:55, BartC wrote:
> On 14/05/2015 17:29, Marko Rauhamaa wrote:
>> BartC <bc at freeuk.com>:
>>
>>> That's a shame because I wanted to tinker with the main dispatcher
>>> loop to try and find out what exactly is making it slow. Nothing that
>>> seems obvious at first sight.
>>
>> My guess is the main culprit is attribute lookup in two ways:
>>
>>   * Each object attribute reference involves a dictionary lookup.
>>
>>   * Each method call involves *two* dictionary lookups plus an object
>>     creation.
>>
>> Tell us what you find out.
>
> I'm just starting but I can tell you that it isn't because debug mode
> (Py_DEBUG defined) was left on by mistake!
>
> What is interesting however is that on the very simple test I'm doing (a
> while loop incrementing a variable up to 100 million), the timings under
> Windows are:
>
> Python 2.5       9.2 seconds
> Python 3.1      13.1
> Python 3.4.3    17.0
> Python 3.4.3    14.3 (under Ubuntu on same machine, using the version
>                        I built today)
>
> That's quite a big range!
>
> PyPy does it in 0.7 seconds. The same program within my own *simple*
> bytecode interpreter (not for Python) has a fastest time of 1.5 seconds
> but makes use of ASM. A version 100% in (gcc) C can manage 2 seconds.
>
> So far I haven't find anything that explains the discrepancy (the
> languages are different, mine is simpler, but the Python code isn't
> doing anything that complicated, only LOAD_FASTs and such, and LOAD_FAST
> is apparently just an array access.
>
> But the nearly 2:1 difference between new and old Python versions is
> also intriguing.
>
> def whiletest():
> 	i=0
> 	while i<=100000000:
> 		i=i+1
>
> whiletest()
>
Python 2.x has int and long; Python 3 has int, which is the old 'long'.
Try Python 2 with longs.