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<!-- The actual name of your proposed change page should look something like: Changes/Your_Change_Proposal_Name.  This keeps all change proposals in the same namespace -->
<!-- The actual name of your proposed change page should look something like: Changes/Your_Change_Proposal_Name.  This keeps all change proposals in the same namespace -->


= Python built with -O3 <!-- The name of your change proposal --> =
= Python built with gcc -O3 <!-- The name of your change proposal --> =


{{Change_Proposal_Banner}}


== Summary ==
== Summary ==
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This only impacts the interpreter and Python standard library, not any 3rd party extension modules built as RPM or on developer machines.
This only impacts the interpreter and Python standard library, not any 3rd party extension modules built as RPM or on developer machines.
This aligns with the way Python is built upstream.
This aligns with the way Python is built upstream.
According to our performance measurements, it makes Python significantly faster.
According to our performance measurements, it makes Python significantly faster (pyperformance geometric mean: 1.04x faster).


== Owner ==
== Owner ==
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== Current status ==
== Current status ==
[[Category:ChangePageIncomplete]]
[[Category:ChangeAcceptedF41]]
<!-- When your change proposal page is completed and ready for review and announcement -->
<!-- When your change proposal page is completed and ready for review and announcement -->
<!-- remove Category:ChangePageIncomplete and change it to Category:ChangeReadyForWrangler -->
<!-- remove Category:ChangePageIncomplete and change it to Category:ChangeReadyForWrangler -->
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ON_QA -> change is fully code complete
ON_QA -> change is fully code complete
-->
-->
* [<will be assigned by the Wrangler> devel thread]
* [https://lists.fedoraproject.org/archives/list/devel-announce@lists.fedoraproject.org/thread/D7Y6GYNL62LCER6GPOA2VQ3DBX3WOYQ6/ Announced]
* FESCo issue: <will be assigned by the Wrangler>
* [https://discussion.fedoraproject.org/t/f41-change-proposal-python-built-with-gcc-03-self-contained/112743 Discussion Thread]
* Tracker bug: <will be assigned by the Wrangler>
* FESCo issue: [https://pagure.io/fesco/issue/3202 #3202]
* Release notes tracker: <will be assigned by the Wrangler>
* Tracker bug: [https://bugzilla.redhat.com/show_bug.cgi?id=2279768 #2279768]
* Release notes tracker: [https://gitlab.com/fedora/docs/fedora-linux-documentation/release-notes/-/issues/134 #134]


== Detailed Description ==
== Detailed Description ==
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''> Overriding these flags for performance optimizations (for instance, `-O3` instead of `-O2`) is generally discouraged. If you can present benchmarks that show a significant speedup for this particular code, this could be revisited on a case-by-case basis.''
''> Overriding these flags for performance optimizations (for instance, `-O3` instead of `-O2`) is generally discouraged. If you can present benchmarks that show a significant speedup for this particular code, this could be revisited on a case-by-case basis.''


This change proposal presents such benchmarks and and presents a case for Python to use `-O3`.
This change proposal presents such benchmarks and a case for Python to use `-O3`.


This change is limited to CPython interpreter and extension modules from the Python standard library only thanks to [[Changes/Python_Extension_Flags_Reduction]] (since Fedora 39). Other Python extension modules will remain bulidng as before, e.g. in RPM packages, they will still be built with `-O2`, unless Fedora changes that globally. The extension modules built with `-O2` still work with Python built with `-O2`.
This change is limited to CPython interpreter and extension modules from the Python standard library only thanks to [[Changes/Python_Extension_Flags_Reduction]] (since Fedora 39). Other Python extension modules will remain bulidng as before, e.g. in RPM packages, they will still be built with `-O2`, unless Fedora changes that globally. The extension modules built with `-O2` still work with Python built with `-O3`.
 
=== Amendment: Flag for user-built extension modules ===
 
{{admon/important|This section was added after the change proposal was approved. It was approved by the Fedora Engineering Steering Committee separatelly.}}
 
When this change was originally proposed, the expectation was that the C flags for building Python extension modules other than modules from the Python standard library would not be changed.
 
* Python extension modules built in Fedora RPM packages were built with `-O2` before this change and would continue to be built that way (for packages other than Python itself).
* Python extension modules built outside of Fedora RPM packages were built with no `-O` flag before this change and would continue to be built that way.
 
However, after implementing the change proposal, it was accidentally changed so the '''Python extension modules built outside of Fedora RPM packages are built with the `-O3` flag'''. This was not originally intended, yet the change owners believe we should keep it that way because it makes Fedora's Python closer to upstream Python and because it makes Fedora more competitive with other platforms on CIs and similar systems.
 
For more details, see https://lists.fedoraproject.org/archives/list/python-devel@lists.fedoraproject.org/thread/2IXTGNASAVR3NNHKFCOIC27CMFA6RJRH/


== Feedback ==
== Feedback ==
<!-- Summarize the feedback from the community and address why you chose not to accept proposed alternatives. This section is optional for all change proposals but is strongly suggested. Incorporating feedback here as it is raised gives FESCo a clearer view of your proposal and leaves a good record for the future. If you get no feedback, that is useful to note in this section as well. For innovative or possibly controversial ideas, consider collecting feedback before you file the change proposal. -->
<!-- Summarize the feedback from the community and address why you chose not to accept proposed alternatives. This section is optional for all change proposals but is strongly suggested. Incorporating feedback here as it is raised gives FESCo a clearer view of your proposal and leaves a good record for the future. If you get no feedback, that is useful to note in this section as well. For innovative or possibly controversial ideas, consider collecting feedback before you file the change proposal. -->
Questions asked and answered:
=== How much larger is Python at -O3 compared to -O2? ===
-O2 RPM size:
*python3-3.12.2-3.fc41.x86_64            32638
*python3-libs-3.12.2-3.fc41.x86_64    42888846
-O3 RPM size:
*python3-3.12.2-3.O3.fc41.x86_64        32638
*python3-libs-3.12.2-3.O3.fc41.x86_64 43389702
Difference of python3-libs:
500856 == '''489 kB''' = 1.1678 % increase in size of pytohn3-libs itself or '''1.1669 %''' of python3-libs+python3 combined size.


== Benefit to Fedora ==
== Benefit to Fedora ==
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-->
-->


Upstream already builds Python with `-O3` by default. Fedora's Python built with `-O3` is faster:
Upstream already builds Python with `-O3` by default. Fedora's Python built with `-O3` is faster (1.04x):


{| class="wikitable sortable"
{| class="wikitable sortable"
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|-
|-
| xml_etree_process                || 106 ms      || 98.6 ms  || 1.08x faster || Significant (t=46.73)   
| xml_etree_process                || 106 ms      || 98.6 ms  || 1.08x faster || Significant (t=46.73)   
|-
| Geometric mean                  ||              ||          || 1.04x faster ||
|}
|}


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The benchmark was performed on Python 3.12 because it uses 3rd party Python packages lacking support for Python 3.13. Once it is possible to run such a benchmark for Python 3.13, we will do so.
The benchmark was performed on Python 3.12 because it uses 3rd party Python packages lacking support for Python 3.13. Once it is possible to run such a benchmark for Python 3.13, we will do so.


The benchmark was performed on x86_64. Until somebody presents a contradicting benchmark, we belive the change makes sense on all architectures.
The benchmark was performed on x86_64. Until somebody presents a contradicting benchmark (or gives explicit reason for us to measure it), we believe the change makes sense on all architectures.
 
Benchmark attempt in Koji on all architectures shows good results on all architectures, for details, see https://discussion.fedoraproject.org/t/f41-change-proposal-python-built-with-gcc-03-self-contained/112743/13


== Scope ==
== Scope ==
* Proposal owners:
* Proposal owners:
** Change python3.13 to build with `-O3` instead of `-O2`
** Change python3.13 to build with `-O3` instead of `-O2` https://src.fedoraproject.org/rpms/python3.13/pull-request/58
** Backport the change to older Pythons if desired
** Backport the change to older Pythons if desired
<!-- What work do the feature owners have to accomplish to complete the feature in time for release?  Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?-->
<!-- What work do the feature owners have to accomplish to complete the feature in time for release?  Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?-->
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<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
 
None expected.


== How To Test ==
== How To Test ==
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<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
To verify this change has landed, inspect the build.log of python3.13. It should be built with `gcc ... -O3`.
To test this change, test Fedora as you would normally do and assert there are no regressions.
Run benchmarks, and report slowdowns if found.




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  - Green has been scientifically proven to be the most relaxing color. The move to a default background color of green with green text will result in Fedora users being the most relaxed users of any operating system.
  - Green has been scientifically proven to be the most relaxing color. The move to a default background color of green with green text will result in Fedora users being the most relaxed users of any operating system.
-->
-->
Faster Python, faster Fedora.


== Dependencies ==
== Dependencies ==
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<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
<!-- REQUIRED FOR SYSTEM WIDE CHANGES -->


* [[Changes/Python_Extension_Flags_Reduction]] landed in Fedora 39
* [[Changes/Python3.13]] is expected to land in Fedora 41. If not, we will apply this on Python 3.12.


== Contingency Plan ==
== Contingency Plan ==


<!-- If you cannot complete your feature by the final development freeze, what is the backup plan?  This might be as simple as "Revert the shipped configuration".  Or it might not (e.g. rebuilding a number of dependent packages).  If you feature is not completed in time we want to assure others that other parts of Fedora will not be in jeopardy.  -->
<!-- If you cannot complete your feature by the final development freeze, what is the backup plan?  This might be as simple as "Revert the shipped configuration".  Or it might not (e.g. rebuilding a number of dependent packages).  If you feature is not completed in time we want to assure others that other parts of Fedora will not be in jeopardy.  -->
* Contingency mechanism: (What to do?  Who will do it?) N/A (not a System Wide Change) <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
* Contingency mechanism: revert the change, rebuild Python <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
<!-- When is the last time the contingency mechanism can be put in place?  This will typically be the beta freeze. -->
<!-- When is the last time the contingency mechanism can be put in place?  This will typically be the beta freeze. -->
* Contingency deadline: N/A (not a System Wide Change) <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
* Contingency deadline: Final Freeze <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
<!-- Does finishing this feature block the release, or can we ship with the feature in incomplete state? -->
<!-- Does finishing this feature block the release, or can we ship with the feature in incomplete state? -->
* Blocks release? N/A (not a System Wide Change), Yes/No <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
* Blocks release? No <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->




Latest revision as of 14:27, 14 October 2024


Python built with gcc -O3

Summary

Instead of Fedora's default -O2 compiler flag, we will use -O3 to build CPython. This only impacts the interpreter and Python standard library, not any 3rd party extension modules built as RPM or on developer machines. This aligns with the way Python is built upstream. According to our performance measurements, it makes Python significantly faster (pyperformance geometric mean: 1.04x faster).

Owner


Current status

Detailed Description

We will replace the -O2 compiler flag with -O3 when building the python3.13 package. This change may be backported to older Pythons if desired. Python 3.13 should be the main Python version in Fedora 41+.

The Fedora packaging guidelines about compiler flags explicitly say:

> Overriding these flags for performance optimizations (for instance, -O3 instead of -O2) is generally discouraged. If you can present benchmarks that show a significant speedup for this particular code, this could be revisited on a case-by-case basis.

This change proposal presents such benchmarks and a case for Python to use -O3.

This change is limited to CPython interpreter and extension modules from the Python standard library only thanks to Changes/Python_Extension_Flags_Reduction (since Fedora 39). Other Python extension modules will remain bulidng as before, e.g. in RPM packages, they will still be built with -O2, unless Fedora changes that globally. The extension modules built with -O2 still work with Python built with -O3.

Amendment: Flag for user-built extension modules

This section was added after the change proposal was approved. It was approved by the Fedora Engineering Steering Committee separatelly.

When this change was originally proposed, the expectation was that the C flags for building Python extension modules other than modules from the Python standard library would not be changed.

  • Python extension modules built in Fedora RPM packages were built with -O2 before this change and would continue to be built that way (for packages other than Python itself).
  • Python extension modules built outside of Fedora RPM packages were built with no -O flag before this change and would continue to be built that way.

However, after implementing the change proposal, it was accidentally changed so the Python extension modules built outside of Fedora RPM packages are built with the -O3 flag. This was not originally intended, yet the change owners believe we should keep it that way because it makes Fedora's Python closer to upstream Python and because it makes Fedora more competitive with other platforms on CIs and similar systems.

For more details, see https://lists.fedoraproject.org/archives/list/python-devel@lists.fedoraproject.org/thread/2IXTGNASAVR3NNHKFCOIC27CMFA6RJRH/

Feedback

Questions asked and answered:

How much larger is Python at -O3 compared to -O2?

-O2 RPM size:

  • python3-3.12.2-3.fc41.x86_64 32638
  • python3-libs-3.12.2-3.fc41.x86_64 42888846

-O3 RPM size:

  • python3-3.12.2-3.O3.fc41.x86_64 32638
  • python3-libs-3.12.2-3.O3.fc41.x86_64 43389702

Difference of python3-libs:

500856 == 489 kB = 1.1678 % increase in size of pytohn3-libs itself or 1.1669 % of python3-libs+python3 combined size.

Benefit to Fedora

Upstream already builds Python with -O3 by default. Fedora's Python built with -O3 is faster (1.04x):

Benchmark with python3.12-3.12.2-3.fc41
Benchmark -O2 -O3 Change Significance
2to3 465 ms 446 ms 1.04x faster Significant (t=21.72)
async_generators 853 ms 784 ms 1.09x faster Significant (t=36.61)
async_tree_cpu_io_mixed 1.19 sec 1.11 sec 1.08x faster Significant (t=13.38)
async_tree_cpu_io_mixed_tg 1.17 sec 1.09 sec 1.08x faster Significant (t=18.69)
async_tree_eager 202 ms 189 ms 1.07x faster Significant (t=7.99)
async_tree_eager_cpu_io_mixed 727 ms 664 ms 1.09x faster Significant (t=18.56)
async_tree_eager_cpu_io_mixed_tg 633 ms 558 ms 1.13x faster Significant (t=24.53)
async_tree_eager_io 1.72 sec 1.68 sec 1.03x faster Significant (t=6.13)
async_tree_eager_io_tg 1.65 sec 1.62 sec 1.02x faster Significant (t=4.65)
async_tree_eager_memoization 437 ms 422 ms 1.04x faster Significant (t=5.09)
async_tree_eager_memoization_tg 330 ms 322 ms 1.03x faster Significant (t=2.60)
async_tree_eager_tg 137 ms 125 ms 1.09x faster Significant (t=16.94)
async_tree_io 1.64 sec 1.60 sec 1.02x faster Significant (t=9.49)
async_tree_io_tg 1.65 sec 1.61 sec 1.02x faster Not significant
async_tree_memoization 895 ms 871 ms 1.03x faster Significant (t=3.73)
async_tree_memoization_tg 848 ms 836 ms 1.01x faster Not significant
async_tree_none 718 ms 700 ms 1.03x faster Significant (t=6.90)
async_tree_none_tg 686 ms 659 ms 1.04x faster Significant (t=13.11)
asyncio_tcp 757 ms 748 ms 1.01x faster Not significant
asyncio_tcp_ssl 2.58 sec 2.56 sec 1.01x faster Not significant
asyncio_websockets 419 ms 418 ms 1.00x faster Not significant
bench_mp_pool 10.7 ms 10.7 ms 1.00x faster Not significant
bench_thread_pool 1.62 ms 1.61 ms 1.01x faster Not significant
chameleon 12.2 ms 12.0 ms 1.02x faster Not significant
chaos 113 ms 105 ms 1.07x faster Significant (t=46.23)
comprehensions 37.4 us 35.1 us 1.07x faster Significant (t=49.72)
coroutines 42.4 ms 41.4 ms 1.02x faster Significant (t=18.68)
coverage 109 ms 104 ms 1.05x faster Significant (t=33.91)
create_gc_cycles 1.84 ms 1.79 ms 1.02x faster Significant (t=5.50)
crypto_pyaes 141 ms 127 ms 1.11x faster Significant (t=86.61)
dask 766 ms 769 ms 1.00x slower Not significant
deepcopy 619 us 614 us 1.01x faster Not significant
deepcopy_memo 71.3 us 68.3 us 1.04x faster Significant (t=26.58)
deepcopy_reduce 5.62 us 5.56 us 1.01x faster Not significant
deltablue 5.76 ms 5.49 ms 1.05x faster Significant (t=7.97)
django_template 62.8 ms 59.7 ms 1.05x faster Significant (t=27.05)
docutils 4.38 sec 4.29 sec 1.02x faster Significant (t=11.25)
fannkuch 706 ms 667 ms 1.06x faster Significant (t=75.80)
float 144 ms 137 ms 1.05x faster Significant (t=24.66)
gc_traversal 5.73 ms 5.81 ms 1.01x slower Not significant
generators 56.0 ms 58.2 ms 1.04x slower Significant (t=-16.25)
genshi_text 40.8 ms 39.5 ms 1.03x faster Significant (t=17.64)
genshi_xml 88.2 ms 86.3 ms 1.02x faster Significant (t=6.96)
go 223 ms 217 ms 1.03x faster Significant (t=19.92)
hexiom 10.3 ms 9.76 ms 1.05x faster Significant (t=42.15)
html5lib 109 ms 108 ms 1.01x faster Not significant
json_dumps 17.4 ms 16.3 ms 1.06x faster Significant (t=45.38)
json_loads 44.2 us 42.3 us 1.04x faster Significant (t=27.71)
logging_format 12.9 us 12.4 us 1.04x faster Significant (t=9.81)
logging_silent 176 ns 174 ns 1.01x faster Not significant
logging_simple 11.4 us 11.0 us 1.03x faster Significant (t=9.94)
mako 19.2 ms 18.1 ms 1.06x faster Significant (t=54.89)
mdp 4.46 sec 4.33 sec 1.03x faster Significant (t=30.14)
meteor_contest 189 ms 167 ms 1.13x faster Significant (t=60.31)
nbody 157 ms 153 ms 1.03x faster Significant (t=4.34)
nqueens 153 ms 140 ms 1.09x faster Significant (t=63.60)
pathlib 32.9 ms 32.6 ms 1.01x faster Not significant
pickle 18.6 us 16.0 us 1.16x faster Significant (t=23.88)
pickle_dict 45.8 us 44.6 us 1.03x faster Significant (t=16.51)
pickle_list 6.86 us 6.59 us 1.04x faster Significant (t=19.65)
pickle_pure_python 515 us 505 us 1.02x faster Not significant
pidigits 285 ms 284 ms 1.00x faster Not significant
pprint_pformat 2.72 sec 2.54 sec 1.07x faster Significant (t=40.28)
pprint_safe_repr 1.34 sec 1.25 sec 1.08x faster Significant (t=58.43)
pyflate 738 ms 724 ms 1.02x faster Not significant
python_startup 15.5 ms 15.3 ms 1.01x faster Not significant
python_startup_no_site 11.2 ms 11.0 ms 1.01x faster Not significant
raytrace 549 ms 514 ms 1.07x faster Significant (t=45.37)
regex_compile 245 ms 233 ms 1.05x faster Significant (t=13.30)
regex_dna 269 ms 268 ms 1.00x faster Not significant
regex_effbot 4.83 ms 4.95 ms 1.03x slower Significant (t=-12.52)
regex_v8 33.7 ms 33.1 ms 1.02x faster Not significant
richards 75.7 ms 71.9 ms 1.05x faster Significant (t=18.30)
richards_super 85.2 ms 81.4 ms 1.05x faster Significant (t=31.25)
scimark_fft 662 ms 587 ms 1.13x faster Significant (t=71.10)
scimark_lu 199 ms 190 ms 1.04x faster Significant (t=26.77)
scimark_monte_carlo 123 ms 117 ms 1.05x faster Significant (t=37.45)
scimark_sor 217 ms 210 ms 1.04x faster Significant (t=10.68)
scimark_sparse_mat_mult 8.51 ms 7.42 ms 1.15x faster Significant (t=62.99)
spectral_norm 196 ms 183 ms 1.07x faster Significant (t=95.78)
sqlalchemy_declarative 239 ms 234 ms 1.02x faster Significant (t=4.81)
sqlalchemy_imperative 33.1 ms 33.4 ms 1.01x slower Not significant
sqlglot_normalize 197 ms 187 ms 1.05x faster Significant (t=39.81)
sqlglot_optimize 97.1 ms 91.3 ms 1.06x faster Significant (t=47.14)
sqlglot_parse 2.29 ms 2.18 ms 1.05x faster Significant (t=14.70)
sqlglot_transpile 2.79 ms 2.67 ms 1.04x faster Significant (t=11.76)
sqlite_synth 3.97 us 3.90 us 1.02x faster Not significant
sympy_expand 833 ms 802 ms 1.04x faster Significant (t=19.41)
sympy_integrate 34.7 ms 33.8 ms 1.03x faster Significant (t=9.99)
sympy_str 511 ms 489 ms 1.04x faster Significant (t=18.17)
sympy_sum 286 ms 278 ms 1.03x faster Significant (t=14.46)
telco 12.6 ms 11.7 ms 1.08x faster Significant (t=9.31)
tomli_loads 3.91 sec 3.56 sec 1.10x faster Significant (t=46.29)
tornado_http 213 ms 212 ms 1.01x faster Not significant
typing_runtime_protocols 214 us 196 us 1.09x faster Significant (t=24.74)
unpack_sequence 70.5 ns 66.0 ns 1.07x faster Significant (t=8.58)
unpickle 24.3 us 22.0 us 1.10x faster Significant (t=10.67)
unpickle_list 7.44 us 8.61 us 1.16x slower Significant (t=-45.10)
unpickle_pure_python 390 us 360 us 1.08x faster Significant (t=37.48)
xml_etree_generate 160 ms 145 ms 1.10x faster Significant (t=44.33)
xml_etree_iterparse 189 ms 180 ms 1.05x faster Significant (t=20.16)
xml_etree_parse 275 ms 257 ms 1.07x faster Significant (t=20.58)
xml_etree_process 106 ms 98.6 ms 1.08x faster Significant (t=46.73)
Geometric mean 1.04x faster

Generated by pyperformance run -o Ox.json and pyperformance compare -O table O2.json O3.json on Fedora 40 x86_64 with rawhide-built Python, python3.12-3.12.2-3.fc41, on Lenovo X1 Carbon 3rd gen.

The benchmark was performed on Python 3.12 because it uses 3rd party Python packages lacking support for Python 3.13. Once it is possible to run such a benchmark for Python 3.13, we will do so.

The benchmark was performed on x86_64. Until somebody presents a contradicting benchmark (or gives explicit reason for us to measure it), we believe the change makes sense on all architectures.

Benchmark attempt in Koji on all architectures shows good results on all architectures, for details, see https://discussion.fedoraproject.org/t/f41-change-proposal-python-built-with-gcc-03-self-contained/112743/13

Scope

  • Other developers: no action expected, report bugs when found
  • Release engineering: no action expected
  • Policies and guidelines: this change is following the spirit of the guidelines
  • Trademark approval: not needed for this Change
  • Alignment with Community Initiatives: faster Python, happier users, more contributors?

Upgrade/compatibility impact

None expected.

How To Test

To verify this change has landed, inspect the build.log of python3.13. It should be built with gcc ... -O3.

To test this change, test Fedora as you would normally do and assert there are no regressions.

Run benchmarks, and report slowdowns if found.


User Experience

Faster Python, faster Fedora.

Dependencies

Contingency Plan

  • Contingency mechanism: revert the change, rebuild Python
  • Contingency deadline: Final Freeze
  • Blocks release? No


Documentation

N/A (not a System Wide Change)

Release Notes

Retrieved from "https://fedoraproject.org/w/index.php?title=Changes/Python_built_with_gcc_O3&oldid=722409"