[pypy-dev] PyPy is much slower than CPython example / question

Stefan Behnel stefan_ml at behnel.de
Sat Jul 9 06:26:46 CEST 2011

Armin Rigo, 08.07.2011 11:18:
> Before attacking the problem with the JIT, we should understand better
> why PyPy is 4-8 times slower than CPython.  Normally you'd expect the
> factor to be at most 2.  I suppose the answer is that our
> itertools.repeat() is bad for some reason.

You shouldn't forget that itertools contains extremely well optimised C 
code. I recently tried to (algorithmically) optimise the pure Python 
implementations from the CPython docs for Cython, and ended up with timings 
between 10% faster and 50% slower. It's actually hard to reach up to the 
raw power of hand tuned C code here.


Given that some of the functions don't execute anything more than a couple 
of assembly instructions per cycle, you'll have to send a really well tuned 
high level implementation into the race to even come close. I would expect 
that PyPy's implementation simply wasn't written for that.

That being said, it would be nice to have an itertools micro benchmark for 
the common Python test suite.


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