[issue42471] Slowdown in socket tests noticed since Py3.8

[Ronald Oussoren]

Change by Ronald Oussoren :


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resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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[issue42471] Slowdown in socket tests noticed since Py3.8

[Terry J. Reedy]

Terry J. Reedy  added the comment:

Should this be closed as 'not a bug'?

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nosy: +terry.reedy

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[issue42471] Slowdown in socket tests noticed since Py3.8

[Bert JW Regeer]

Bert JW Regeer  added the comment:

Ned: You are correct, I hadn't even considered that as a potential issue. Added 
a context to grab the fork multiprocessing context and we are back to the speed 
it was before.

This slowdown is pretty huge for just changing the way the process is forked.

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[issue42471] Slowdown in socket tests noticed since Py3.8

[Ned Deily]

Ned Deily  added the comment:

Do your tests use the multiprocessing module? As of 3.8, the default start 
method for multiprocessing on macOS was changed from “fork” to “spawn”:

https://docs.python.org/3.8/library/multiprocessing.html#contexts-and-start-methods

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nosy: +ned.deily, ronaldoussoren

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[issue42471] Slowdown in socket tests noticed since Py3.8

[Bert JW Regeer]

New submission from Bert JW Regeer :

I am being fairly vague here, but it is mainly because I don't know the best 
way to reduce the test cases down to pinpoint the problem.

I maintain Waitress, a pure Python HTTP server, and ever since Python 3.8 
there's been a marked slowdown of the functional tests.

Python 3.6 on my MacBook Pro M1 Rosetta: 15.91s to run the entire test suite, 
similar slow tests as Py37. So not included.

Python 3.7 on my MacBook Pro M1 Rosetta: 15.57s to run the entire test suite

Slowest tests on Py37 is:

3.10s call tests/test_functional.py::SleepyThreadTests::test_it
1.01s call 
tests/test_channel.py::TestHTTPChannelLookahead::test_client_disconnect
0.41s call tests/test_wasyncore.py::DispatcherWithSendTests::test_send
0.17s call 
tests/test_wasyncore.py::TestAPI_UseIPv6Poll::test_handle_close_after_conn_broken
0.11s call tests/test_wasyncore.py::TestAPI_UseIPv4Select::test_handle_read
0.11s call 
tests/test_wasyncore.py::TestAPI_UseIPv4Select::test_handle_close_after_conn_broken
0.11s call 
tests/test_wasyncore.py::TestAPI_UseIPv4Poll::test_handle_close_after_conn_broken
0.11s call 
tests/test_wasyncore.py::TestAPI_UseUnixSocketsPoll::test_handle_close_after_conn_broken
0.11s call 
tests/test_wasyncore.py::TestAPI_UseIPv6Select::test_handle_close_after_conn_broken
0.11s call tests/test_wasyncore.py::TestAPI_UseIPv4Select::test_handle_close

Python 3.8 on my MacBook Pro M1 Rosetta: 44.33 seconds to run the entire test 
suite

3.34s call tests/test_functional.py::SleepyThreadTests::test_it
1.01s call 
tests/test_channel.py::TestHTTPChannelLookahead::test_client_disconnect
0.41s call tests/test_wasyncore.py::DispatcherWithSendTests::test_send
0.40s call 
tests/test_functional.py::TcpInternalServerErrorTests::test_before_start_response_http_11_close
0.36s call 
tests/test_functional.py::TcpInternalServerErrorTests::test_before_start_response_http_11
0.35s call 
tests/test_functional.py::UnixWriteCallbackTests::test_no_content_length
0.34s call 
tests/test_functional.py::TcpInternalServerErrorTests::test_after_write_cb
0.33s call 
tests/test_functional.py::TcpInternalServerErrorTests::test_after_start_response_http11_close
0.32s call 
tests/test_functional.py::TcpFileWrapperTests::test_filelike_nocl_http10
0.32s call 
tests/test_functional.py::TcpFileWrapperTests::test_filelike_http10

Python 3.9 on my MacBook Pro M1 Rosetta: 41.93 seconds

3.28s call tests/test_functional.py::SleepyThreadTests::test_it
1.01s call 
tests/test_channel.py::TestHTTPChannelLookahead::test_client_disconnect
0.41s call tests/test_wasyncore.py::DispatcherWithSendTests::test_send
0.36s call tests/test_functional.py::TcpWriteCallbackTests::test_short_body
0.33s call 
tests/test_functional.py::TcpFileWrapperTests::test_notfilelike_nocl_http10
0.32s call 
tests/test_functional.py::TcpEchoTests::test_chunking_request_without_content
0.32s call tests/test_functional.py::TcpEchoTests::test_date_and_server
0.31s call 
tests/test_functional.py::TcpBadContentLengthTests::test_long_body
0.30s call 
tests/test_functional.py::TcpEchoTests::test_broken_chunked_encoding_missing_chunk_end
0.30s call 
tests/test_functional.py::TcpTooLargeTests::test_request_body_too_large_with_wrong_cl_http10

This is very visible too in the test times on Github actions:

https://github.com/Pylons/waitress/runs/1335343659?check_suite_focus=true 
(Python 3.7, running tox takes 40 seconds)

https://github.com/Pylons/waitress/runs/1335343690?check_suite_focus=true 
(Python 3.8, running tox takes 3m and 42seconds)

Although GitHub actions are not always reliable since it is shared 
infrastructure and you never know who your neighbors are, but the same issue 
holds across all of the Mac devices I own (2017 MacBook Pro i7, 2012 Mac Mini 
i7). Just as an extra data point, my 2017 MacBook Pro runs the py39 tests in 67 
seconds, and the py37 tests in 26 seconds.

The problem is that I don't know where to begin attempting figure out what is 
going on. So I am shooting my shot here in the bug tracker. How can I help 
debug this/track this down so that we can get rid of the regression and speed 
things back up?

Open source project: https://github.com/Pylons/waitress
Uses pytest to run tests, tox is the easiest way to accomplish this.

--
messages: 381891
nosy: X-Istence
priority: normal
severity: normal
status: open
title: Slowdown in socket tests noticed since Py3.8
versions: Python 3.8, Python 3.9

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