[Python-Dev] Possible performance regression

[Raymond Hettinger]

> On Feb 24, 2019, at 10:06 PM, Eric Snow <ericsnowcurrently at gmail.com> wrote:
> 
> I'll look into it in more depth tomorrow.  FWIW, I have a few commits
> in the range you described, so I want to make sure I didn't slow
> things down for us. :)

Thanks for looking into it.

FWIW, I can consistently reproduce the results several times in row.  Here's the bash script I'm using:

#!/bin/bash

make clean
./configure
make                                                        # Apple LLVM version 10.0.0 (clang-1000.11.45.5)

for i in `seq 1 3`;
do
    git checkout d610116a2e48b55788b62e11f2e6956af06b3de0   # Go back to 2/23
    make                                                    # Rebuild
    sleep 30                                                # Let the system get quiet and cool
    echo '---- baseline ---' >> results.txt                 # Label output
    ./python.exe Tools/scripts/var_access_benchmark.py >> results.txt   # Run benchmark

    git checkout 16323cb2c3d315e02637cebebdc5ff46be32ecdf   # Go to end-of-day 2/24
    make                                                    # Rebuild
    sleep 30                                                # Let the system get quiet and cool
    echo '---- end of day ---' >> results.txt               # Label output
    ./python.exe Tools/scripts/var_access_benchmark.py >> results.txt   # Run benchmark


> 
> -eric
> 
> 
> * commit 175421b58cc97a2555e474f479f30a6c5d2250b0 (HEAD)
> | Author: Pablo Galindo <Pablogsal at gmail.com>
> | Date:   Sat Feb 23 03:02:06 2019 +0000
> |
> |     bpo-36016: Add generation option to gc.getobjects() (GH-11909)
> 
> $ ./python Tools/scripts/var_access_benchmark.py
> Variable and attribute read access:
>  18.1 ns       read_local
>  19.4 ns       read_nonlocal

These timings are several times larger than they should be.  Perhaps you're running a debug build?  Or perhaps 32-bit? Or on VM or some such.  Something looks way off because I'm getting 4 and 5 ns on my 2013 Haswell laptop.



Raymond