[issue23106] Remove smalltable from set objects

[Raymond Hettinger]

New submission from Raymond Hettinger:

This tracker item is here to record my efforts to re-evaluate whether we were getting much if any benefit from the smalltable in set objects.

Removing the smalltable special case and instead using a memory allocation had the following effects:

* Nice simplification of the code, greatly improving the clarity of the functions for resizing, clearing, and swapping.

* Reduced the memory consumption for sets that were already using memory allocated tables (saved the memory cost of the unused smalltable).

* Nearly doubled the time to allocate and free set objects (see timings below for CLang and GCC).

As a percentage change, the time penalty seems like a killer, but then we're talking about only 1/10th of a μsec per set.



# CLANG #########

~/base_cp/python.exe -m timeit -s 'from itertools import repeat, starmap' 'list(starmap(set, repeat((), 250000)))'
10 loops, best of 3: 39.1 msec per loop
~/cpython/python.exe -m timeit -s 'from itertools import repeat, starmap' 'list(starmap(set, repeat((), 250000)))'
10 loops, best of 3: 76.7 msec per loop
~/base_cp/python.exe -m timeit -s 'from itertools import repeat, starmap' 'list(starmap(set, repeat((), 250000)))'
10 loops, best of 3: 38.8 msec per loop
~/cpython/python.exe -m timeit -s 'from itertools import repeat, starmap' 'list(starmap(set, repeat((), 250000)))'
10 loops, best of 3: 76.6 msec per loop

~/base_cp/python.exe -m timeit '{1,2,3}'
10000000 loops, best of 3: 0.0964 usec per loop
~/cpython/python.exe -m timeit '{1,2,3}'
10000000 loops, best of 3: 0.148 usec per loop
~/base_cp/python.exe -m timeit '{1,2,3}'
10000000 loops, best of 3: 0.0964 usec per loop
~/cpython/python.exe -m timeit '{1,2,3}'
10000000 loops, best of 3: 0.149 usec per loop

# GCC-4.9 ########
~/base_cp $ ~/base_cp/python.exe -m timeit '{1,2,3}'
10000000 loops, best of 3: 0.0701 usec per loop
~/base_cp $ ~/cpython/python.exe -m timeit '{1,2,3}'
10000000 loops, best of 3: 0.155 usec per loop
~/base_cp $ ~/base_cp/python.exe -m timeit '{1,2,3}'
10000000 loops, best of 3: 0.0691 usec per loop
~/base_cp $ ~/cpython/python.exe -m timeit '{1,2,3}'
10000000 loops, best of 3: 0.157 usec per loop

~/base_cp $ ~/base_cp/python.exe -m timeit -s 'from itertools import repeat, starmap' 'list(starmap(set, repeat((), 250000)))'
10 loops, best of 3: 34.6 msec per loop
~/base_cp $ ~/cpython/python.exe -m timeit -s 'from itertools import repeat, starmap' 'list(starmap(set, repeat((), 250000)))'
10 loops, best of 3: 77 msec per loop
~/base_cp $ ~/base_cp/python.exe -m timeit -s 'from itertools import repeat, starmap' 'list(starmap(set, repeat((), 250000)))'
10 loops, best of 3: 34.1 msec per loop
~/base_cp $ ~/cpython/python.exe -m timeit -s 'from itertools import repeat, starmap' 'list(starmap(set, repeat((), 250000)))'
10 loops, best of 3: 77.3 msec per loop

----------
assignee: rhettinger
components: Interpreter Core
files: no_smalltable2.diff
keywords: patch
messages: 233068
nosy: rhettinger
priority: low
severity: normal
status: open
title: Remove smalltable from set objects
type: performance
versions: Python 3.5
Added file: http://bugs.python.org/file37535/no_smalltable2.diff

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue23106>
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