[Python-Dev] Python 3.6 dict becomes compact and gets a private version; and keywords become ordered (original) (raw)

INADA Naoki songofacandy at gmail.com
Thu Sep 15 05:23:02 EDT 2016

On Thu, Sep 15, 2016 at 5:57 PM Victor Stinner <victor.stinner at gmail.com> wrote:

2016-09-15 10:02 GMT+02:00 INADA Naoki <songofacandy at gmail.com>: > In my environ: > > ~/local/python-master/bin/python3 -m timeit -s "d = > dict.fromkeys(range(10**6))" 'list(d)'

Stooooop! Please stop using timeit, it's lying! * You must not use the minimum but average or median * You must run a microbenchmark in multiple processes to test different randomized hash functions and different memory layouts In short: you should use my perf module. http://perf.readthedocs.io/en/latest/cli.html#timeit I'm sorry. Changing habit is bit difficult. I'll use it in next time.

I ran microbench 3~5 times and confirm the result is stable before posting result. And when difference is smaller than 10%, I don't believe the result.

The memory layout and the hash function have a major important on such microbenchmark: https://haypo.github.io/journey-to-stable-benchmark-average.html

In this microbench, hash randomization is not important, because key of dict is int. (It means iterating dict doesn't cause random memory access in old dict implementation too.)

> Both Python is built without neither --with-optimizations or make_ _> profile-opt. That's bad :-) For most reliable benchmarks, it's better to use LTO+PGO compilation.

LTO+PGO may make performance of git pull && make unstable. PGO clean build takes tooo long time for such a quick benchmark. So I don't want to use PGO in such a quick benchmark.

And Python doesn't provide way to use LTO without PGO.... -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20160915/38b684a4/attachment.html>

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