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* Cygwin TCP slow
@ 2016-11-29  1:25 Daniel Havey
  2016-11-29  5:56 ` Brian Inglis
  0 siblings, 1 reply; 10+ messages in thread
From: Daniel Havey @ 2016-11-29  1:25 UTC (permalink / raw)
  To: cygwin

Hello,
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.

thanxs ;^)
...Daniel

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^ permalink raw reply	[flat|nested] 10+ messages in thread

end of thread, other threads:[~2017-01-04 21:33 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-11-29  1:25 Cygwin TCP slow Daniel Havey
2016-11-29  5:56 ` Brian Inglis
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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