Thanks for testing. Oddly, I just tested it in Linux (Ubuntu), and get the same results as you -- Python 2.7.13 outperforms 3 (3.5.3 in my case) by a few percent. And even under a Virtualbox VM it takes 3.4 and 3.6 seconds, compared to ~5s on the host macOS operating system. Very odd. I guess that means Virtualbox is very good, and that clang/LLVM is not as good at optimizing the Python VM as gcc is.
I can't find anything majorly different about my macOS Python 2 and 3 builds. Both look like they have PGO turned on (from sysconfig.get_config_vars()). Both have HAVE_COMPUTED_GOTOS=1 but USE_COMPUTED_GOTOS=0 for some reason. My Python 2 version is the macOS system version (/usr/local/bin/python2), whereas my Python3 version is from "brew install", so that's probably the difference, though still doesn't explain exactly why. -Ben On Mon, Jul 24, 2017 at 1:49 PM, Wang, Peter Xihong < peter.xihong.w...@intel.com> wrote: > Hi Ben, > > Out of curiosity with a quick experiment, I ran your pentomino.py with > 2.7.12 PGO+LTO build (Ubuntu OS 16.04.2 LTS default at /usr/bin/python), > and compared with 3.7.0 alpha1 PGO+LTO (which I built a while ago), on my > SkyLake processor based desktop, and 2.7 outperforms 3.7 by 3.5%. > On your 2.5 GHz i7 system, I'd recommend making sure the 2 Python binaries > you are comparing are in equal footings (compiled with same optimization > PGO+LTO). > > Thanks, > > Peter > > > > -----Original Message----- > From: Python-Dev [mailto:python-dev-bounces+peter.xihong.wang=intel.com@ > python.org] On Behalf Of Nathaniel Smith > Sent: Tuesday, July 18, 2017 7:00 PM > To: Ben Hoyt <benh...@gmail.com> > Cc: Python-Dev <python-dev@python.org> > Subject: Re: [Python-Dev] Program runs in 12s on Python 2.7, but 5s on > Python 3.5 -- why so much difference? > > I'd probably start with a regular C-level profiler, like perf or > callgrind. They're not very useful for comparing two versions of code > written in Python, but here the Python code is the same (modulo changes in > the stdlib), and it's changes in the interpreter's C code that probably > make the difference. > > On Tue, Jul 18, 2017 at 9:03 AM, Ben Hoyt <benh...@gmail.com> wrote: > > Hi folks, > > > > (Not entirely sure this is the right place for this question, but > > hopefully it's of interest to several folks.) > > > > A few days ago I posted a note in response to Victor Stinner's > > articles on his CPython contributions, noting that I wrote a program > > that ran in 11.7 seconds on Python 2.7, but only takes 5.1 seconds on > > Python 3.5 (on my 2.5 GHz macOS i7), more than 2x as fast. Obviously > > this is a Good Thing, but I'm curious as to why there's so much > difference. > > > > The program is a pentomino puzzle solver, and it works via code > > generation, generating a ton of nested "if" statements, so I believe > > it's exercising the Python bytecode interpreter heavily. Obviously > > there have been some big optimizations to make this happen, but I'm > > curious what the main improvements are that are causing this much > difference. > > > > There's a writeup about my program here, with benchmarks at the bottom: > > http://benhoyt.com/writings/python-pentomino/ > > > > This is the generated Python code that's being exercised: > > https://github.com/benhoyt/python-pentomino/blob/master/generated_solv > > e.py > > > > For reference, on Python 3.6 it runs in 4.6 seconds (same on Python > > 3.7 alpha). This smallish increase from Python 3.5 to Python 3.6 was > > more expected to me due to the bytecode changing to wordcode in 3.6. > > > > I tried using cProfile on both Python versions, but that didn't say > > much, because the functions being called aren't taking the majority of > the time. > > How does one benchmark at a lower level, or otherwise explain what's > > going on here? > > > > Thanks, > > Ben > > > > _______________________________________________ > > Python-Dev mailing list > > Python-Dev@python.org > > https://mail.python.org/mailman/listinfo/python-dev > > Unsubscribe: > > https://mail.python.org/mailman/options/python-dev/njs%40pobox.com > > > > > > -- > Nathaniel J. Smith -- https://vorpus.org ______________________________ > _________________ > Python-Dev mailing list > Python-Dev@python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: https://mail.python.org/mailman/options/python-dev/ > peter.xihong.wang%40intel.com >
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