Add the SIO_LOOPBACK_FAST_PATH option to socket.ioctl

[DanielStokes]

BPO	26536
Nosy	@pfmoore, @pitrou, @tjguk, @berkerpeksag, @vadmium, @zware, @zooba
Files	loopback_fast_path.patch loopback_fast_path_v2.patch loopback_fast_path_test.zip loopback_fast_path_v3.patch

^{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 = 'https://github.com/zooba'
closed_at = <Date 2016-06-18.13:40:54.454>
created_at = <Date 2016-03-11.03:15:26.080>
labels = ['extension-modules', 'type-feature', 'OS-windows']
title = 'Add the SIO_LOOPBACK_FAST_PATH option to socket.ioctl'
updated_at = <Date 2016-06-18.17:17:47.218>
user = 'https://bugs.python.org/DanielStokes'

bugs.python.org fields:

activity = <Date 2016-06-18.17:17:47.218>
actor = 'steve.dower'
assignee = 'steve.dower'
closed = True
closed_date = <Date 2016-06-18.13:40:54.454>
closer = 'berker.peksag'
components = ['Extension Modules', 'Windows']
creation = <Date 2016-03-11.03:15:26.080>
creator = 'Daniel Stokes'
dependencies = []
files = ['42124', '42888', '42895', '42908']
hgrepos = []
issue_num = 26536
keywords = ['patch']
message_count = 16.0
messages = ['261539', '264326', '264335', '265805', '265845', '265847', '265906', '268738', '268739', '268777', '268801', '268802', '268803', '268805', '268806', '268816']
nosy_count = 9.0
nosy_names = ['paul.moore', 'pitrou', 'tim.golden', 'python-dev', 'berker.peksag', 'martin.panter', 'zach.ware', 'steve.dower', 'Daniel Stokes']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue26536'
versions = ['Python 3.6']

[DanielStokes]

Adding the SIO_LOOPBACK_FAST_PATH option to socket.ioctl on Windows allows Windows users to enable the loopback fast path option available on Windows 8+. This allows for much better TCP loopback performance on Windows.

For more information on TCP Loopback Fast Path, see:

• https://msdn.microsoft.com/en-us/library/windows/desktop/jj841212%28v=vs.85%29.aspx
• http://blogs.technet.com/b/wincat/archive/2012/12/05/fast-tcp-loopback-performance-and-low-latency-with-windows-server-2012-tcp-loopback-fast-path.aspx

[DanielStokes]

The "Lifecycle of a Patch" document recommends pinging an issue after a month of no review. I do not see any special ping option, so I am assuming that means to post a comment.

To help with code review I tried to keep this change very similar to a previous similar change: http://bugs.python.org/issue6971

[berkerpeksag]

Thanks for pinging, Daniel. I'm not a Windows user so I can't test the patch, but I left some review comments on Rietveld: http://bugs.python.org/review/26536/

[DanielStokes]

Thank you for the review. I have made the changes suggested in the code and I have uploaded a new patch.

[DanielStokes]

I have added a zip containing a simple server and client to test the patch with. With loopback fast path enabled, I get 3-5x more throughput on my Windows 10 computer with an AMD 900 series chipset.

[berkerpeksag]

Thanks for the test script. I left some minor comments about loopback_fast_path_v2.patch on Rietveld.

[DanielStokes]

I have uploaded a new patch with the suggested changes, thanks for the review.

[python-dev]

New changeset f8957c755c7a by Steve Dower in branch 'default':
Issue bpo-26536: socket.ioctl now supports SIO_LOOPBACK_FAST_PATH. Patch by Daniel Stokes.
https://hg.python.org/cpython/rev/f8957c755c7a

[zooba]

All looked good to me, and as far as I could see all of Berker's feedback was addressed, so consider it in!

[vadmium]

This is failing on Windows 7 buildbots:

http://buildbot.python.org/all/builders/AMD64%20Windows7%20SP1%203.x/builds/7849/steps/test/logs/stdio
======================================================================
ERROR: test_sio_loopback_fast_path (test.test_socket.GeneralModuleTests)
----------------------------------------------------------------------

Traceback (most recent call last):
  File "C:\buildbot.python.org\3.x.kloth-win64\build\lib\test\test_socket.py", line 1226, in test_sio_loopback_fast_path
    s.ioctl(socket.SIO_LOOPBACK_FAST_PATH, True)
OSError: [WinError 10045] The attempted operation is not supported for the type of object referenced

[python-dev]

New changeset e8b10ed64e63 by Berker Peksag in branch 'default':
Issue bpo-26536: Skip test_sio_loopback_fast_path under Windows 7
https://hg.python.org/cpython/rev/e8b10ed64e63

[berkerpeksag]

It looks like SIO_LOOPBACK_FAST_PATH is also defined in older Windows versions. I updated the test to skip if SIO_LOOPBACK_FAST_PATH is defined and exc.winerror is WSAEOPNOTSUPP. Buildbot is now green: http://buildbot.python.org/all/builders/AMD64%20Windows7%20SP1%203.x/builds/7855

Please reopen if I did something wrong.

[python-dev]

New changeset 213c240cce0a by Berker Peksag in branch 'default':
Issue bpo-26536: Use spaces instead of tabs
https://hg.python.org/cpython/rev/213c240cce0a

[zooba]

That'll handle the test fine, though I wonder whether we should try and conditionally define the constant at runtime?

Probably at least want to add a note to the docs about Win 8 being the minimum, especially since so many people are still on 7.

[berkerpeksag]

That'll handle the test fine, though I wonder whether we should try and conditionally define the constant at runtime?

+1. Is it safe to use IsWindows8OrGreater()?

[zooba]

That's the best function to use.