My setup
Linux Debian 11 running in Oracle Virtual Box
Python version: 3.8.14
Docker version 20.10.22, build 3a2c30b
RAM for Debian 11 OS: 17 GB
Running directly on Debian 11 OS, timings consistently stay around 385 msec
$ python -m timeit "sum(range(8000000))"
1 loop, best of 5: 385 msec per loop
$ python -m timeit "sum(range(8000000))"
1 loop, best of 5: 384 msec per loop
While executing the same command with docker it takes around 795 msec
docker run --rm -it --entrypoint bash python:3.8-slim-buster
:/# python -m timeit "sum(range(8000000))"
1 loop, best of 5: 795 msec per loop
:/# python -m timeit "sum(range(8000000))"
1 loop, best of 5: 797 msec per loop
My actual program, which is doing CPU intensive operation, is showing similar result, it take double time to execute inside docker.
Any idea/hint why execution timings are higher in docker?