Improve Telnetlib's throughput

[martinkirch]

BPO	46740
Nosy	@terryjreedy, @JelleZijlstra, @martinkirch
PRs	bpo-46740: speedup telnetlib's buffer transfers #31449

^{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 = None
created_at = <Date 2022-02-13.20:17:40.706>
labels = ['library', '3.10', 'performance']
title = "Improve Telnetlib's throughput"
updated_at = <Date 2022-02-20.15:04:10.574>
user = 'https://github.com/martinkirch'

bugs.python.org fields:

activity = <Date 2022-02-20.15:04:10.574>
actor = 'martin_kirch'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2022-02-13.20:17:40.706>
creator = 'martin_kirch'
dependencies = []
files = []
hgrepos = []
issue_num = 46740
keywords = ['patch']
message_count = 3.0
messages = ['413195', '413206', '413509']
nosy_count = 3.0
nosy_names = ['terry.reedy', 'JelleZijlstra', 'martin_kirch']
pr_nums = ['31449']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'resource usage'
url = 'https://bugs.python.org/issue46740'
versions = ['Python 3.10']

[martinkirch]

While using telnetlib I sometimes received unusually "large" messages (around 1Mb) from another process on the same machine, and was surprised read_until took more than a second. After instrumenting I discovered such messages were received at roughly 500kbyte/s.

I think this low throughput comes from two implementation details:

• Telnet.fill_rawq is calling self.sock.recv(50), whereas 4096 is now recommended
• the Telnet.process_rawq method is transferring from raw queue to cooked queue by appending byte per byte.

For the latter, transferring by slices looks much faster (I'm measuring at least 5x). I'm preparing a PR.

[JelleZijlstra]

Note that telnetlib is being proposed for deprecation in PEP-594. You may be better off using a third-party telnet implementation; the PEP lists https://pypi.org/project/telnetlib3/ and https://pypi.org/project/Exscript/.

[terryjreedy]

Even if deprecated, it will be around for at least 2 versions. A patch now might be worthwhile, but I don't know who would review it.

[hugovk]

(Linking to #91217 for future reference.)

[AlexWaygood]

Even if deprecated, it will be around for at least 2 versions. A patch now might be worthwhile, but I don't know who would review it.

telnetlib is listed as having no active maintainer in PEP 594, and is now officially deprecated following the Steering Council's acceptance of the PEP. As such, unless there are any core developers who want to volunteer to review PR #9121 (which has now been open for nearly two months without core review), I think the issue and the PR should probably be closed.

(Cc. @martinkirch)

[hugovk]

As such, unless there are any core developers who want to volunteer to review PR #9121 (which has now been open for nearly two months without core review), ...

Correction, it's this PR: #31449

[martinkirch]

OK, closed the PR ; but I can only comment this issue.