I don't know if this qualifies as a simple test case, but if you don't already have wireshark, get it from https://www.wireshark.org/download.html get iperf-2.0.9.tar.gz from https://sourceforge.net/projects/iperf2/files/ change the setsockopt calls on lines 125 & 132 of src/tcp_window_size.c to rc = 0;
./configure --prefix=/usr/local make && make install start wireshark & add a column for bytes in flight: edit / preferences appearance / columns click on the "+" button to get a new row double click on the "New Column", type BIF double click the empty bit in the Fields column type tcp.an which pulls up a pick list; click on tcp.analysis.bytes_in_flight click on OK find a public iperf server -- I got lucky & found one ~65ms away, so thruput is going to be constrained by the 130ms round trip time. start the wireshark capture iperf -c <host name> when it's done stop the capture & click on the BIF column header What I get is a max bytes in flight of 66560 ----recompile iperf using the windows cross-compiler make clean make distclean ./configure --prefix=/usr/local --build=i686-pc-cygwin --host=i686-w64-mingw32 make && make install start capturing iperf -c <host name> when it's done stop the capture & sort on the BIF column What I get is a max bytes in flight of 196608 So, for me, it's about a 3X difference between the native & cygwin app. If the problem really is in net.cc as the OP said, have a look at https://cygwin.com/git/gitweb.cgi?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/net.cc;h=e4805d3e11c3cea09b1cdfa27170dfe626265125;hb=HEAD starting at line 587 /* Raise default buffer sizes (instead of WinSock default 8K). I think starting with Windows Vista the default is tcp autotuning. So unless there's some other reason for setting the send/receive buffer it seems that cygwin apps would be better off going with the defaults. Lee -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
