CPython dev sprint 2017: Startup speedup: profiling startup time

gistfile1.txt

See:
  https://public.etherpad-mozilla.org/p/cpython-dev-sprint-2017
  
- background: https://lwn.net/Articles/730915/

- profiling of import

- DTrace probes for module import start/done
    https://github.com/nascheme/cpython/tree/dtrace-module-import
    https://gist.github.com/nascheme/c1cece36a3369926ee93cecc3d024179
    https://gist.github.com/nascheme/0bff5c49bb6b518f5ce23a9aea27f14b

- Findings: importlib is slow (written in Python) but is already well optimized
and no low hanging fruit there

- marshal.load looked expensive but compile with gcc -O fixed that

- some modules are slow, os -> _collections_abc, could do more things lazily
(e.g. _Environ)

- trial program not too bad, about 18 ms on my MacBook

- further work: lazy loading of modules supported by AST (hard work to do by hand), lazy loading of module parts