From: Brian Inglis <Brian.Inglis@SystematicSw.ab.ca>
To: cygwin@cygwin.com
Subject: Re: Cygwin TCP slow
Date: Tue, 29 Nov 2016 05:56:00 -0000 [thread overview]
Message-ID: <5adc37f5-608b-6c1f-6d14-83343c82dc9f@SystematicSw.ab.ca> (raw)
In-Reply-To: <CAO1c0AT52ZzCKc3yD_7eX6ri4VubrTb5L+X-4vHWoXBAX2jsfw@mail.gmail.com>
On 2016-11-28 12:54, Daniel Havey wrote:
> We have had complaints from several large hardware vendors that
> Windows networking is slow for apps like iperf that are used to
> measure throughput. Iperf on Windows is compiled against the
> cygwin1.dll. We have root caused the problem to a couple of lines of
> code in net.cc that set SO_RCVBUF and SO_SNDBUF to about 200KB.
>
> The theoretical window/RTT plot for the buffer size set by Cygwin
> (0x34000 = 200KB) gives us:
> 1ms -> 1703Mbps
> 2ms -> 851Mbps
> 3ms -> 567Mbps
> 4ms -> 425Mbps
> 5ms -> 340Mbps
> 6ms -> 283Mbps
> 7ms -> 243Mbps
> 8ms -> 212Mbps
> 9ms -> 189Mbps
> 10ms -> 170Mbps
> 20ms -> 85Mbps
> 40ms -> 42Mbps
> 60ms -> 28Mbps
> 80ms -> 21Mbps
>
> We have confirmed this by experiment and also confirmed that the
> limitation goes away if the buffers are not manually set. Windows has
> autotuning and when the buffers are set manually the autotuning is
> disabled. This is causing the throughput limitation. So we would
> like to formally ask that you please not manually set SO_RCVBUF or
> SO_SNDBUF.
See problem reports: http://cygwin.com/problems.html
Provide STC, patches, attach cygcheck -svr output?
Links to downstream bug reports, testing, results?
Note that Cygwin iperf is year old 2.0.5.
--
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada
--
Problem reports: http://cygwin.com/problems.html
FAQ: http://cygwin.com/faq/
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next prev parent reply other threads:[~2016-11-28 20:51 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-29 1:25 Daniel Havey
2016-11-29 5:56 ` Brian Inglis [this message]
2016-11-30 9:16 ` Daniel Havey
2016-11-30 10:09 ` Sam Habiel
2016-11-30 10:44 ` Brian Inglis
2016-11-30 16:00 ` Lee
[not found] ` <CAD8GWss1zb1J7m3Knf1TGuAPcVKQVNFXgt2uX02o_Z08ZOfEOw@mail.gmail.com>
2016-12-02 20:29 ` Daniel Havey
2016-12-02 22:37 ` Brian Inglis
2017-01-04 21:33 ` Daniel Havey
2016-12-02 23:08 ` Mark Geisert
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