[Python-Dev] Program runs in 12s on Python 2.7, but 5s on Python 3.5 -- why so much difference? (original) (raw)
Ben Hoyt benhoyt at gmail.com
Tue Jul 18 21:41:38 EDT 2017
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Thanks, Nick -- that's interesting. I just saw the extra JUMP_FORWARD and JUMP_ABSOLUTE instructions on my commute home (I guess those are something Python 3.x optimizes away).
VERY strangely, on Windows Python 2.7 is faster! Comparing 64-bit Python 2.7.12 against Python 3.5.3 on my Windows 10 laptop:
- Python 2.7.12: 4.088s
- Python 3.5.3: 5.792s
I'm pretty sure MSVC/Windows doesn't support computed gotos, but that doesn't explain why 3.5 is so much faster than 2.7 on Mac. I have yet to try it on Linux.
-Ben
On Tue, Jul 18, 2017 at 9:35 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:
On 19 July 2017 at 02:18, Antoine Pitrou <solipsis at pitrou.net> wrote: > On Tue, 18 Jul 2017 12:03:36 -0400 > Ben Hoyt <benhoyt at gmail.com> wrote: >> 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. > > A first step would be to see if the generated bytecode has changed > substantially.
Scanning over them, the Python 2.7 bytecode appears to have many more JUMPFORWARD and JUMPABSOLUTE opcodes than appear in the 3.6 version (I didn't dump them into a Counter instance to tally them properly though, since 2.7's dis module is missing the structured opcode iteration APIs). With the shift to wordcode, the overall size of the bytecode is also significantly smaller: >>> len(co.coconsts[0].cocode) # 2.7 14427 >>> len(co.coconsts[0].cocode) # 3.6 11850 However, I'm not aware of any Python profilers that currently offer opcode level profiling - the closest would probably be VMProf's JIT profiling, and that aspect of VMProf is currently PyPy specific (although could presumably be extended to CPython 3.6+ by way of the opcode evaluation hook). Cheers, Nick. -- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia
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