https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=609d2b22afc63d80029a4fe85e64b51c84ccae08
commit 609d2b22afc63d80029a4fe85e64b51c84ccae08
Author: Corinna Vinschen
Date: Fri Feb 3 21:46:01 2017 +0100
Fix limited Internet speeds caused by inappropriate socket buffering
Don't set SO_RCVBUF/SO_SNDBUF to fixed values, thus disabling autotuning.
Patch modeled after a patch suggestion from Daniel Havey
in https://cygwin.com/ml/cygwin-patches/2017-q1/msg00010.html:
At Windows we love what you are doing with Cygwin. However, we have
been getting reports from our hardware vendors that iperf is slow on
Windows. Iperf is of course compiled against the cygwin1.dll and we
believe we have traced the problem down to the function fdsock in
net.cc. SO_RCVBUF and SO_SNDBUF are being manually set. The comments
indicate that the idea was to increase the buffer size, but, this code
must have been written long ago because Windows has used autotuning
for a very long time now. Please do not manually set SO_RCVBUF or
SO_SNDBUF as this will limit your internet speed.
I am providing a patch, an STC and my cygcheck -svr output. Hope we
can fix this. Please let me know if I can help further.
Simple Test Case:
I have a script that pings 4 times and then iperfs for 10 seconds to
debit.k-net.fr
With patch
$ bash buffer_test.sh 178.250.209.22
usage: bash buffer_test.sh
Pinging 178.250.209.22 with 32 bytes of data:
Reply from 178.250.209.22: bytes=32 time=167ms TTL=34
Reply from 178.250.209.22: bytes=32 time=173ms TTL=34
Reply from 178.250.209.22: bytes=32 time=173ms TTL=34
Reply from 178.250.209.22: bytes=32 time=169ms TTL=34
Ping statistics for 178.250.209.22:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 167ms, Maximum = 173ms, Average = 170ms
Client connecting to 178.250.209.22, TCP port 5001
TCP window size: 64.0 KByte (default)
[ 3] local 10.137.196.108 port 58512 connected with 178.250.209.22 port
5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0- 1.0 sec 768 KBytes 6.29 Mbits/sec
[ 3] 1.0- 2.0 sec 9.25 MBytes 77.6 Mbits/sec
[ 3] 2.0- 3.0 sec 18.0 MBytes 151 Mbits/sec
[ 3] 3.0- 4.0 sec 18.0 MBytes 151 Mbits/sec
[ 3] 4.0- 5.0 sec 18.0 MBytes 151 Mbits/sec
[ 3] 5.0- 6.0 sec 18.0 MBytes 151 Mbits/sec
[ 3] 6.0- 7.0 sec 18.0 MBytes 151 Mbits/sec
[ 3] 7.0- 8.0 sec 18.0 MBytes 151 Mbits/sec
[ 3] 8.0- 9.0 sec 18.0 MBytes 151 Mbits/sec
[ 3] 9.0-10.0 sec 18.0 MBytes 151 Mbits/sec
[ 3] 0.0-10.0 sec 154 MBytes 129 Mbits/sec
Without patch:
dahavey@DMH-DESKTOP ~
$ bash buffer_test.sh 178.250.209.22
Pinging 178.250.209.22 with 32 bytes of data:
Reply from 178.250.209.22: bytes=32 time=168ms TTL=34
Reply from 178.250.209.22: bytes=32 time=167ms TTL=34
Reply from 178.250.209.22: bytes=32 time=170ms TTL=34
Reply from 178.250.209.22: bytes=32 time=169ms TTL=34
Ping statistics for 178.250.209.22:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 167ms, Maximum = 170ms, Average = 168ms
Client connecting to 178.250.209.22, TCP port 5001
TCP window size: 208 KByte (default)
[ 3] local 10.137.196.108 port 58443 connected with 178.250.209.22 port
5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0- 1.0 sec 512 KBytes 4.19 Mbits/sec
[ 3] 1.0- 2.0 sec 1.50 MBytes 12.6 Mbits/sec
[ 3] 2.0- 3.0 sec 1.50 MBytes 12.6 Mbits/sec
[ 3] 3.0- 4.0 sec 1.50 MBytes 12.6 Mbits/sec
[ 3] 4.0- 5.0 sec 1.50 MBytes 12.6 Mbits/sec
[ 3] 5.0- 6.0 sec 1.50 MBytes 12.6 Mbits/sec
[ 3] 6.0- 7.0 sec 1.50 MBytes 12.6 Mbits/sec
[ 3] 7.0- 8.0 sec 1.50 MBytes 12.6 Mbits/sec
[ 3] 8.0- 9.0 sec 1.50 MBytes 12.6 Mbits/sec
[ 3] 9.0-10.0 sec 1.50 MBytes 12.6 Mbits/sec
[ 3] 0.0-10.1 sec 14.1 MBytes 11.7 Mbits/sec
The output shows that the RTT from my machine to the iperf server is
similar in both cases (about 170ms) however with the patch the
throughput averages 129 Mbps while without the patch the throughput
only averages 11.7 Mbps. If we calculate the maximum throughput using
Bandwidth = Queue/RTT we get (212992 * 8)/0.170 = 10.0231 Mbps. This
is just about what iperf is showing us without the patch since the
buffer size is set to 212992 I believe that the buffer size is
limiting the thro
