[Python-ideas] Why CPython is still behind in performance for some widely used patterns ?

Victor Stinner victor.stinner at gmail.com
Fri Jan 26 18:28:12 EST 2018


Well, I wrote https://faster-cpython.readthedocs.io/ website to answer
to such question.

See for example https://faster-cpython.readthedocs.io/mutable.html
"Everything in Python is mutable".


2018-01-26 22:35 GMT+01:00 Pau Freixes <pfreixes at gmail.com>:
> Hi,
> This mail is the consequence of a true story, a story where CPython
> got defeated by Javascript, Java, C# and Go.
> One of the teams of the company where Im working had a kind of
> benchmark to compare the different languages on top of their
> respective "official" web servers such as Node.js, Aiohttp, Dropwizard
> and so on.  The test by itself was pretty simple and tried to test the
> happy path of the logic, a piece of code that fetches N rules from
> another system and then apply them to X whatevers also fetched from
> another system, something like that
> def filter(rule, whatever):
>     if rule.x in whatever.x:
>         return True
> rules = get_rules()
> whatevers = get_whatevers()
> for rule in rules:
>     for whatever in whatevers:
>         if filter(rule, whatever):
>             cnt = cnt + 1
> return cnt
> The performance of Python compared with the other languages was almost
> x10 times slower. It's true that they didn't optimize the code, but
> they did not for any language having for all of them the same cost in
> terms of iterations.
> Once I saw the code I proposed a pair of changes, remove the call to
> the filter function making it "inline" and caching the rule's
> attributes, something like that
> for rule in rules:
>     x = rule.x
>     for whatever in whatevers:
>         if x in whatever.x:
>             cnt += 1
> The performance of the CPython boosted x3/x4 just doing these "silly" things.
> The case of the rule cache IMHO is very striking, we have plenty
> examples in many repositories where the caching of none local
> variables is a widely used pattern, why hasn't been considered a way
> to do it implicitly and by default?
> The case of the slowness to call functions in CPython is quite
> recurrent and looks like its an unsolved problem at all.
> Sure I'm missing many things, and I do not have all of the
> information. This mail wants to get all of this information that might
> help me to understand why we are here - CPython - regarding this two
> slow patterns.
> This could be considered an unimportant thing, but its more relevant
> than someone could expect, at least IMHO. If the default code that you
> can write in a language is by default slow and exists an alternative
> to make it faster, this language is doing something wrong.
> BTW: pypy looks like is immunized [1]
> [1] https://gist.github.com/pfreixes/d60d00761093c3bdaf29da025a004582
> --
> --pau
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