eventlet monkey_patch'ed subprocess is 10 times slower in IO than original

[dkolvakh]

$ uname -a
Linux dk-VirtualBox-tmp 5.15.0-84-generic #93-Ubuntu SMP Tue Sep 5 17:16:10 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

$ python -V
Python 3.10.12

$ pip freeze
alabaster==0.7.12
apt-clone==0.2.1
apturl==0.5.2
Babel==2.8.0
beautifulsoup4==4.10.0
blinker==1.4
Brlapi==0.8.3
cachetools==5.3.0
ccsm==0.9.14.1
certifi==2020.6.20
chardet==5.1.0
click==8.0.3
colorama==0.4.6
command-not-found==0.3
compizconfig-python==0.9.14.1
configobj==5.0.6
cryptography==3.4.8
cupshelpers==1.0
dbus-python==1.2.18
defer==1.0.6
distlib==0.3.6
distro==1.7.0
dnspython==2.4.2
docutils==0.17.1
dulwich==0.21.5
eventlet==0.33.3
eyeD3==0.8.10
filelock==3.10.7
greenlet==2.0.2
grpcio==1.30.2
httplib2==0.20.2
idna==3.3
ifaddr==0.1.7
imagesize==1.3.0
IMDbPY==2021.4.18
importlib-metadata==4.6.4
jeepney==0.7.1
Jinja2==3.0.3
keyring==23.5.0
launchpadlib==1.10.16
lazr.restfulclient==0.14.4
lazr.uri==1.0.6
louis==3.20.0
Mako==1.1.3
MarkupSafe==2.0.1
more-itertools==8.10.0
netaddr==0.8.0
netifaces==0.11.0
oauthlib==3.2.0
onboard==1.4.1
openstackdocstheme==3.2.0
packaging==23.0
pbr==5.11.1
pexpect==4.8.0
Pillow==9.0.1
platformdirs==3.2.0
pluggy==1.0.0
protobuf==3.12.4
psutil==5.9.0
ptyprocess==0.7.0
py==1.10.0
pycairo==1.20.1
pycups==2.0.1
pycurl==7.44.1
pyelftools==0.27
Pygments==2.11.2
PyGObject==3.42.1
PyICU==2.8.1
PyJWT==2.3.0
PyNaCl==1.5.0
pyparsing==2.4.7
pyparted==3.11.7
pyproject_api==1.5.1
python-apt==2.4.0+ubuntu2
python-debian==0.1.43+ubuntu1.1
python-magic==0.4.24
python-xapp==2.2.2
python-xlib==0.29
pytz==2022.1
pyxdg==0.27
PyYAML==5.4.1
reportlab==3.6.8
requests==2.25.1
requests-file==1.5.1
roman==3.3
sbd==1.0.0
SecretStorage==3.3.1
setproctitle==1.2.2
six==1.16.0
snowballstemmer==2.2.0
soupsieve==2.3.1
Sphinx==4.3.2
sphinxcontrib-svg2pdfconverter==1.2.2
systemd-python==234
tldextract==3.1.2
toml==0.10.2
tomli==2.0.1
tox==4.4.8
ubuntu-drivers-common==0.0.0
ufw==0.36.1
Unidecode==1.3.3
urllib3==1.26.5
virtualenv==20.21.0
wadllib==1.3.6
xdg==5
xkit==0.0.0
youtube-dl==2021.12.17
zipp==1.0.0

Cause of the error
During monkey_patch 'eventlet' doesn't care about constants in built-in 'select' module, that's why patched 'subprocess' module falls back from linux-wide 4096 bytes to default and 'safe' 512 bytes for IO buffer trying to lookup for non-existing constant in 'eventlet.green.select' module:

python3.10/subprocess.py:

    # When select or poll has indicated that the file is writable,
    # we can write up to _PIPE_BUF bytes without risk of blocking.
    # POSIX defines PIPE_BUF as >= 512.
    _PIPE_BUF = getattr(select, 'PIPE_BUF', 512)

Steps to reproduce the error
test_write_pipes.py:

import logging
import sys
import time
logging.basicConfig(
    stream=sys.stdout, level=logging.DEBUG,
    format='[%(asctime)s] %(message)s {%(filename)s:%(lineno)d}')
LOG = logging.getLogger(__name__)

WRITE_CHUNK_SIZE = 64 * (1024 ** 2)
IMAGE_FILE_SIZE = WRITE_CHUNK_SIZE * 2


def image_file_read(chunk_size):
    data_len = 0
    while data_len < IMAGE_FILE_SIZE:
        start_time = time.time()
        data = b'*' * chunk_size
        LOG.debug(f'Generated in {(time.time() - start_time):.4f} seconds')
        yield data
        data_len += len(data)


def do_run():
    LOG.debug('START')

    for image_data in image_file_read(WRITE_CHUNK_SIZE):
        args = [
            'dd', 'of=./data_file',
        ]
        write_time = time.time()
        subprocess.run(
            args,
            input=image_data,
            capture_output=True
        )
        LOG.debug(f'Written in {(time.time() - write_time):.4f} seconds')

    LOG.debug('END')
    LOG.debug('===================================')


try:
    import subprocess
    LOG.debug('Use built-in subprocess and select libraries')
    do_run()
finally:
    pass

try:
    import eventlet
    import subprocess

    eventlet.monkey_patch()
    eventlet_patched = eventlet and eventlet.patcher.is_monkey_patched(
        subprocess)
    LOG.debug(f'{eventlet_patched=}')
    LOG.debug('Use patched by eventlet subprocess and select libraries')
    do_run()
finally:
    pass

Result:

$ python3 test_write_pipes.py
[2023-10-06 17:42:49,931] Use built-in subprocess and select libraries {test_write_pipes.py:44}
[2023-10-06 17:42:49,931] START {test_write_pipes.py:24}
[2023-10-06 17:42:49,961] Generated in 0.0298 seconds {test_write_pipes.py:18}
[2023-10-06 17:42:49,967] _PIPE_BUF=4096 {subprocess.py:2005}
[2023-10-06 17:42:51,798] Written in 1.8370 seconds {test_write_pipes.py:36}
[2023-10-06 17:42:51,828] Generated in 0.0297 seconds {test_write_pipes.py:18}
[2023-10-06 17:42:51,834] _PIPE_BUF=4096 {subprocess.py:2005}
[2023-10-06 17:42:53,259] Written in 1.4264 seconds {test_write_pipes.py:36}
[2023-10-06 17:42:53,259] END {test_write_pipes.py:38}
[2023-10-06 17:42:53,259] =================================== {test_write_pipes.py:39}
[2023-10-06 17:42:53,490] eventlet_patched=True {test_write_pipes.py:56}
[2023-10-06 17:42:53,490] Use patched by eventlet subprocess and select libraries {test_write_pipes.py:57}
[2023-10-06 17:42:53,490] START {test_write_pipes.py:24}
[2023-10-06 17:42:53,527] Generated in 0.0360 seconds {test_write_pipes.py:18}
[2023-10-06 17:42:53,531] _PIPE_BUF=512 {subprocess.py:2005}
[2023-10-06 17:43:06,731] Written in 13.2037 seconds {test_write_pipes.py:36}
[2023-10-06 17:43:06,760] Generated in 0.0288 seconds {test_write_pipes.py:18}
[2023-10-06 17:43:06,765] _PIPE_BUF=512 {subprocess.py:2005}
[2023-10-06 17:43:19,503] Written in 12.7389 seconds {test_write_pipes.py:36}
[2023-10-06 17:43:19,503] END {test_write_pipes.py:38}
[2023-10-06 17:43:19,503] =================================== {test_write_pipes.py:39}