Add variable access benchmark to Tools/Scripts

[rhettinger]

BPO	35884
Nosy	@rhettinger, @miss-islington
PRs	bpo-35884: Add variable access benchmarking script #11725 bpo-35884: Add variable access benchmarking script #11725 bpo-35884: Add missing FIFO queue benchmark #11898 bpo-35884: Add string-keys-only microbenchmark for dict access to var_access_benchmark.py #11905

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-02-03.06:55:59.157>
created_at = <Date 2019-02-01.20:19:39.894>
labels = ['3.8', 'performance']
title = 'Add variable access benchmark to Tools/Scripts'
updated_at = <Date 2019-03-25.08:21:01.704>
user = 'https://github.com/rhettinger'

bugs.python.org fields:

activity = <Date 2019-03-25.08:21:01.704>
actor = 'rhettinger'
assignee = 'none'
closed = True
closed_date = <Date 2019-02-03.06:55:59.157>
closer = 'rhettinger'
components = ['Demos and Tools']
creation = <Date 2019-02-01.20:19:39.894>
creator = 'rhettinger'
dependencies = []
files = []
hgrepos = []
issue_num = 35884
keywords = ['patch', 'patch']
message_count = 5.0
messages = ['334716', '334719', '334788', '335718', '338790']
nosy_count = 2.0
nosy_names = ['rhettinger', 'miss-islington']
pr_nums = ['11725', '11725', '11898', '11905']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue35884'
versions = ['Python 3.8']

[rhettinger]

Adding a short script that I've found useful many times over the past decade. It has allowed my to quickly notice performance regressions and has helped identify places in need of optimization work. It is also useful for building a empirical mental model of the relative cost of various kinds of variable access -- this is useful in writing high performance code.

[rhettinger]

Here's what the output looks like (here am comparing a fresh Py3.8 with Clang versus the same build with GCC-8):

$ make distclean && ./configure && make
$ py Tools/scripts/var_access_benchmark.py
Speed of different kinds of variable accesses:
   4.2 μs	read_local
   4.7 μs	read_nonlocal
  13.7 μs	read_global
  18.5 μs	read_builtin
  18.2 μs	read_classvar
  26.8 μs	read_instancevar
  20.3 μs	read_instancevar_slots
  19.1 μs	read_namedtuple
  26.9 μs	read_boundmethod
   4.5 μs	write_local
   4.8 μs	write_nonlocal
  18.8 μs	write_global
  89.9 μs	write_classvar
  37.1 μs	write_instancevar
  25.7 μs	write_instancevar_slots
   0.3 μs	loop_overhead

$ make distclean && ./configure CC=gcc-8 && make
$ py Tools/scripts/var_access_benchmark.py
Speed of different kinds of variable accesses:
   4.0 μs	read_local
   4.2 μs	read_nonlocal
  11.4 μs	read_global
  16.3 μs	read_builtin
  16.4 μs	read_classvar
  24.8 μs	read_instancevar
  20.1 μs	read_instancevar_slots
  16.8 μs	read_namedtuple
  23.2 μs	read_boundmethod
   4.3 μs	write_local
   4.5 μs	write_nonlocal
  15.4 μs	write_global
  89.4 μs	write_classvar
  33.5 μs	write_instancevar
  24.5 μs	write_instancevar_slots
   0.3 μs	loop_overhead

[rhettinger]

New changeset f75d59e by Raymond Hettinger in branch 'master':
bpo-35884: Add variable access benchmarking script (GH-11725)
f75d59e

[miss-islington]

New changeset 43766f8 by Miss Islington (bot) (Raymond Hettinger) in branch 'master':
bpo-35884: Add missing FIFO queue benchmark (GH-11898)
43766f8

[rhettinger]

New changeset 68d228f by Raymond Hettinger (Stefan Behnel) in branch 'master':
bpo-35884: Add string-keys-only microbenchmark for dict access to var_access_benchmark.py (GH-11905)
68d228f