Inada Naoki <songofaca...@gmail.com> added the comment:
> I don't think this should have been done. Conceptually, there is no basis > for presuming key-sharing for new empty dicts -- you can't know what they > would share with. This patch essentially undoes the entire reason for having a pre-allocated minsize dict. If it were deemed to be the norm that applications typically had huge numbers of empty dicts that were never populated, then the correct solution would be a NULL pointer to the table field (as dicts do). It increases massive NULL checks, and possibly cause bugs. > FWIW, the macro benchmarks aren't very informative here because they don't > exercise much of this code. I think there is an over-prioritization of small > space savings at the expense of the intended use cases for dicts. This patch > just forces every dict that gets used to have to convert back from a > key-sharing dict and do a memory allocation and memset(0) in the process. > The whole point of the minsize dict was to avoid that cost in the common case > of small dicts (i.e. passing keyword arguments). Note that there is _PyDict_NewPresized(). When kwargs is empty, this patch increase dict creation speed. When kwargs is not empty, temporary key-sharing table is not used because we use _PyDict_NewPresized() is used. $ ./py.edict bm_edict.py --compare-to ./py.master py.master: ..................... 192 ns +- 7 ns py.edict: ..................... 175 ns +- 4 ns Mean +- std dev: [py.master] 192 ns +- 7 ns -> [py.edict] 175 ns +- 4 ns: 1.10x faster (-9%) py.master: ..................... 269 ns +- 4 ns py.edict: ..................... 273 ns +- 2 ns Mean +- std dev: [py.master] 269 ns +- 4 ns -> [py.edict] 273 ns +- 2 ns: 1.02x slower (+2%) So I don't think net performance of kwargs doesn't get worse. ---------- nosy: -Mark.Shannon _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue30040> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
