GH-88116: Use a compact format to represent end line and column offsets. #91666

markshannon · 2022-04-18T14:07:33Z

Reduces the memory consumption for extended location information to less than half.
Location information now takes ~3.5 bytes per instruction, instead of 8. (Note this is per instruction, not code unit).
All the information is saved in one table, instead of three.

#88116

…ra address info.

Tools/gdb/libpython.py

brandtbucher · 2022-04-19T22:21:38Z

Looks like this results in a 6% memory improvement over main:

Faster (50):
- html5lib: 19.5 MB +- 3818.1 kB -> 14.3 MB +- 1504.1 kB: 1.36x faster
- pickle_dict: 9628.8 kB +- 639.9 kB -> 8825.6 kB +- 21.5 kB: 1.09x faster
- sympy_expand: 59.3 MB +- 15.9 kB -> 54.5 MB +- 40.5 kB: 1.09x faster
- sympy_integrate: 59.2 MB +- 341.5 kB -> 54.4 MB +- 439.2 kB: 1.09x faster
- sympy_str: 60.4 MB +- 16.4 kB -> 55.6 MB +- 34.4 kB: 1.09x faster
- go: 10.5 MB +- 357.3 kB -> 9933.6 kB +- 471.4 kB: 1.08x faster
- deltablue: 10.9 MB +- 153.2 kB -> 10.1 MB +- 183.4 kB: 1.08x faster
- sqlalchemy_declarative: 30.4 MB +- 97.6 kB -> 28.2 MB +- 33.6 kB: 1.08x faster
- meteor_contest: 11.0 MB +- 624.6 kB -> 10.3 MB +- 27.5 kB: 1.08x faster
- chameleon: 20.5 MB +- 101.0 kB -> 19.1 MB +- 164.3 kB: 1.08x faster
- json_dumps: 10.7 MB +- 282.2 kB -> 10172.4 kB +- 353.9 kB: 1.08x faster
- xml_etree_process: 13.2 MB +- 216.1 kB -> 12.2 MB +- 1339.7 kB: 1.08x faster
- unpickle: 9546.4 kB +- 48.9 kB -> 8880.0 kB +- 44.7 kB: 1.08x faster
- json_loads: 8948.8 kB +- 51.2 kB -> 8329.6 kB +- 19.2 kB: 1.07x faster
- fannkuch: 8866.0 kB +- 48.3 kB -> 8264.8 kB +- 43.4 kB: 1.07x faster
- sympy_sum: 67.2 MB +- 3430.4 kB -> 62.6 MB +- 2516.7 kB: 1.07x faster
- django_template: 37.3 MB +- 130.6 kB -> 34.8 MB +- 582.1 kB: 1.07x faster
- logging_silent: 9223.2 kB +- 51.4 kB -> 8618.0 kB +- 51.7 kB: 1.07x faster
- sqlalchemy_imperative: 30.2 MB +- 83.4 kB -> 28.2 MB +- 676.0 kB: 1.07x faster
- pickle_pure_python: 9472.8 kB +- 51.8 kB -> 8865.2 kB +- 34.5 kB: 1.07x faster
- pickle_list: 9458.0 kB +- 48.6 kB -> 8856.4 kB +- 38.9 kB: 1.07x faster
- unpickle_list: 9451.2 kB +- 41.3 kB -> 8850.4 kB +- 50.7 kB: 1.07x faster
- genshi_text: 12.4 MB +- 111.4 kB -> 11.6 MB +- 115.8 kB: 1.07x faster
- raytrace: 9852.4 kB +- 39.3 kB -> 9238.0 kB +- 20.8 kB: 1.07x faster
- pickle: 9450.0 kB +- 21.5 kB -> 8863.2 kB +- 50.6 kB: 1.07x faster
- unpickle_pure_python: 9460.0 kB +- 21.0 kB -> 8875.6 kB +- 45.7 kB: 1.07x faster
- nbody: 9023.6 kB +- 62.0 kB -> 8474.0 kB +- 18.8 kB: 1.06x faster
- regex_compile: 10.0 MB +- 23.3 kB -> 9648.8 kB +- 28.8 kB: 1.06x faster
- chaos: 9804.0 kB +- 46.1 kB -> 9218.8 kB +- 13.1 kB: 1.06x faster
- scimark_monte_carlo: 9552.0 kB +- 55.7 kB -> 8982.4 kB +- 52.3 kB: 1.06x faster
- scimark_sor: 9583.6 kB +- 56.9 kB -> 9017.6 kB +- 69.3 kB: 1.06x faster
- richards: 9411.2 kB +- 16.0 kB -> 8858.8 kB +- 63.3 kB: 1.06x faster
- unpack_sequence: 10.3 MB +- 62.4 kB -> 9914.4 kB +- 41.1 kB: 1.06x faster
- spectral_norm: 8828.8 kB +- 48.4 kB -> 8315.6 kB +- 40.4 kB: 1.06x faster
- scimark_fft: 9686.4 kB +- 55.9 kB -> 9128.8 kB +- 39.8 kB: 1.06x faster
- scimark_sparse_mat_mult: 10115.6 kB +- 25.0 kB -> 9543.6 kB +- 35.0 kB: 1.06x faster
- scimark_lu: 9614.0 kB +- 20.0 kB -> 9076.4 kB +- 31.9 kB: 1.06x faster
- pidigits: 9035.2 kB +- 19.6 kB -> 8532.0 kB +- 31.6 kB: 1.06x faster
- pathlib: 10.1 MB +- 41.3 kB -> 9790.8 kB +- 34.4 kB: 1.06x faster
- tornado_http: 31.4 MB +- 912.5 kB -> 29.7 MB +- 1137.7 kB: 1.06x faster
- crypto_pyaes: 9374.0 kB +- 129.7 kB -> 8869.2 kB +- 114.8 kB: 1.06x faster
- nqueens: 9085.6 kB +- 30.2 kB -> 8605.2 kB +- 53.3 kB: 1.06x faster
- sqlite_synth: 10.9 MB +- 38.3 kB -> 10.3 MB +- 27.4 kB: 1.06x faster
- xml_etree_generate: 13.4 MB +- 319.8 kB -> 12.7 MB +- 366.7 kB: 1.05x faster
- dulwich_log: 15.3 MB +- 97.1 kB -> 14.6 MB +- 82.8 kB: 1.05x faster
- genshi_xml: 12.9 MB +- 120.7 kB -> 12.4 MB +- 12.1 kB: 1.04x faster
- regex_v8: 14.6 MB +- 34.7 kB -> 14.1 MB +- 56.0 kB: 1.04x faster
- python_startup: 11.2 MB +- 28.6 kB -> 10.9 MB +- 41.4 kB: 1.03x faster
- python_startup_no_site: 11.2 MB +- 30.8 kB -> 10.9 MB +- 32.8 kB: 1.03x faster
- 2to3: 22.0 MB +- 51.4 kB -> 21.6 MB +- 64.3 kB: 1.02x faster

Benchmark hidden because not significant (11): float, hexiom, logging_format, logging_simple, mako, pyflate, regex_dna, regex_effbot, telco, xml_etree_parse, xml_etree_iterparse

Geometric mean: 1.06x faster

Objects/codeobject.c

iritkatriel · 2022-04-20T18:00:15Z

Objects/codeobject.c

+        else {
+            int ldelta = get_line_delta(&data[offset]);
+            *output++ = 0xe8 | blength;
+            output += write_signed_varint(output, ldelta);


Is this reimplementing write_location_info_no_column from compile.c?

We could probably get an even tighter representation for the ! code_debug_ranges case (which is presumably the perf critical one). Here we are only using two of the codes, and using ~~a whole byte~~ 4 bits to specify which one. Am I right?

Although there are only two codes, there is the implicit bit of information about whether code_debug_ranges is set.
So there are 6 bits of information in the byte.

Why do we need this extra info in each entry?

Which extra info?

Whether code_debug_ranges is set. It's the same across all entries, no?

I see. If that information is not stored in the entry, then we effectively have two distinct formats.
Which means two different sets of code for creating and parsing the tables.
I doubt that it is worth it.

iritkatriel · 2022-04-21T11:03:28Z

Looks like this results in a 6% memory improvement over main:

I think we need a similar comparison with debug_ranges turned off.

iritkatriel

I think https://github.com/python/cpython/pull/91666/files#r854367808 can be addressed now (replace the 15 by the enum), but the other comments we can look at later.

It would be good in the future to have all the logic about the structure of this table in one place. Currently it's split between compile.c, codeobject.c and the tests. We can look at this (and the exceptions table) as part of the compiler work for 3.12.

We can also think later about an even-more optimised representation for line-numbers-only if we want.

Objects/codeobject.c

vstinner · 2022-04-21T15:16:10Z

Is the documentation up to date? https://docs.python.org/dev/c-api/code.html#c.PyCode_New

Should it be documented in What's New in Python 3.11?

markshannon · 2022-04-21T15:25:25Z

The documentation is correct again, now I've removed the two extra tables. It wasn't before.

markshannon · 2022-04-21T15:27:20Z

No, it is wrong as it is missing the exception table.
Was that documentation ever right? 😞

vstinner · 2022-04-21T17:05:09Z

Was that documentation ever right? disappointed

The Python 3.10 doc looks correct, no? If not, it should be fixed ;-)

https://docs.python.org/3.10/c-api/code.html#c.PyCode_New

pablogsal · 2022-06-09T23:31:33Z

@markshannon There is something wrong with commit 944fffe and the new encoding format. Check out #93662

markshannon added 12 commits April 14, 2022 14:19

Compact debug info. Work in progress.

78cd7a3

Get compact debug table (almost) working.

f603e3f

Remove column table from code objects.

34ec9d9

Remove end-line table from code objects.

6f69354

Remove line table from code objects.

b529306

Remove unused table generation code from compiler.

62228e0

Rename locationtable back to linetable to conform to PEP 626.

ab8cd4f

Use enum values and fix gdb support.

4e1584a

Merge branch 'main' into compact-debug-info

8ec48cf

Document location table format

9783d10

Fix potential memory leak

3020b15

Restore old name for internal API.

b25595b

markshannon requested review from tiran and iritkatriel as code owners April 18, 2022 14:07

bedevere-bot added the awaiting core review label Apr 18, 2022

markshannon added 6 commits April 18, 2022 15:20

Re-run argument clinic

1a2b359

Add NEWS item

70e139f

Remove unnecessary check

baf38d8

Remove a bit of code duplication. Insert bounds check when remove ext…

bcb3309

…ra address info.

Fix handling of missing endline in location info.

3299d06

Fix remove_column_info (correctly this time)

6e0aef9

iritkatriel reviewed Apr 19, 2022

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markshannon mentioned this pull request Apr 21, 2022

Efficient storage of code object debug information faster-cpython/ideas#354

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iritkatriel approved these changes Apr 21, 2022

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Move some logic about location table layout to shared header.

b6b4321

markshannon merged commit 944fffe into python:main Apr 21, 2022

bedevere-bot removed the awaiting merge label Apr 21, 2022

reaperhulk mentioned this pull request Apr 30, 2022

3.11a7 CTracer compilation fails nedbat/coveragepy#1367

Closed

The-Compiler mentioned this pull request May 26, 2022

Objects/codeobject.c:814: retreat: Assertion `bounds->ar_start > 0' failed #93249

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kumaraditya303 mentioned this pull request Jun 6, 2022

Add coverage benchmark python/pyperformance#213

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sobolevn mentioned this pull request Sep 6, 2022

gh-94808: _PyLineTable_StartsLine was not used #96609

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markshannon deleted the compact-debug-info branch September 26, 2023 12:49

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GH-88116: Use a compact format to represent end line and column offsets. #91666

GH-88116: Use a compact format to represent end line and column offsets. #91666

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GH-88116: Use a compact format to represent end line and column offsets. #91666

GH-88116: Use a compact format to represent end line and column offsets. #91666

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