[Python-Dev] PEP 471 Final: os.scandir() merged into Python 3.5

[Ryan Stuart]

Hi Ben,

On Mon, 9 Mar 2015 at 21:58 Ben Hoyt <benhoyt at gmail.com> wrote:

> Note that this benchmark is invalid for a couple of reasons. (...)
>

Thanks a lot for the guidance Ben, greatly appreciated. Just starting to
take an interest in the development of CPython and so something like
running a benchmark seemed like a good a place as any to start.

Since I want to get comfortable with compiling from source I tried this
again. Instead of applying the patch, since the issue is now closed, I just
compiled from the tip of the default branch which at the time
was 94920:0469af231d22. I also didn't configure with --with-pydebug. Here
are the new results:

*Ryans-MacBook-Pro:cpython rstuart$ ./python.exe
~/Workspace/python/scandir/benchmark.py*
Using Python 3.5's builtin os.scandir()
Comparing against builtin version of os.walk()
Priming the system's cache...
Benchmarking walks on /Users/rstuart/Workspace/python/scandir/benchtree,
repeat 1/3...
Benchmarking walks on /Users/rstuart/Workspace/python/scandir/benchtree,
repeat 2/3...
Benchmarking walks on /Users/rstuart/Workspace/python/scandir/benchtree,
repeat 3/3...
os.walk took 0.061s, scandir.walk took 0.012s -- 5.2x as fast

*Ryans-MacBook-Pro:cpython rstuart$ ./python.exe
~/Workspace/python/scandir/benchmark.py -s*
Using Python 3.5's builtin os.scandir()
Comparing against builtin version of os.walk()
Priming the system's cache...
Benchmarking walks on /Users/rstuart/Workspace/python/scandir/benchtree,
repeat 1/3...
Benchmarking walks on /Users/rstuart/Workspace/python/scandir/benchtree,
repeat 2/3...
Benchmarking walks on /Users/rstuart/Workspace/python/scandir/benchtree,
repeat 3/3...
os.walk size 23400, scandir.walk size 23400 -- equal
os.walk took 0.109s, scandir.walk took 0.049s -- 2.2x as fast

This is on a Retina Mid 2012 MacBook Pro with an SSD.

Cheers


> you're compiling Python in debug mode (--with-pydebug), which produces
> significantly slower code in my tests -- for example, on Windows
> benchmark.py is about twice as slow when Python is compiled in debug
> mode.
>
> Second, as the output above shows, benchmark.py is "Using slower
> ctypes version of scandir" and not a C version at all. If os.scandir()
> is available, benchmark.py should use that, so there's something wrong
> here -- maybe the patch didn't apply correctly or maybe you're testing
> with a different version of Python than the one you built?
>
> In any case, the easiest way to test it now is to download Python 3.5
> alpha 2 which just came out:
> https://www.python.org/downloads/release/python-350a2/
>
> I just tried this on my Mac Mini (i5 2.3GHz, 2 GB RAM, HFS+ on
> rotational drive) and got the following results:
>
> Using Python 3.5's builtin os.scandir()
> Comparing against builtin version of os.walk()
> Priming the system's cache...
> Benchmarking walks on benchtree, repeat 1/3...
> Benchmarking walks on benchtree, repeat 2/3...
> Benchmarking walks on benchtree, repeat 3/3...
> os.walk took 0.074s, scandir.walk took 0.016s -- 4.7x as fast
>
> > I then did ./python.exe ~/Workspace/python/scandir/benchmark.py -s and
> got:
>
> Also note that "benchmark.py -s" tests the system os.walk() against a
> get_tree_size() function using scandir's DirEntry.stat().st_size,
> which provides huge gains on Windows (because stat().st_size doesn't
> require on OS call) but only modest gains on POSIX systems, which
> still require an OS stat call to get the size (though not the file
> type, so at least it's only one stat call). I get "2.2x as fast" on my
> Mac for "benchmark.py -s".
>
> -Ben
>
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