Hi Iuliu, On Nov 18 19:30, Iuliu Rus wrote: > Hello, > Google is running Cygwin apps on its 10Gb networks and we are seeing > extremely bad performance in a couple of cases. For example, iperf > with the defaults results in only 10Mbits/sec. > We tracked this down to a combination of non-blocking sockets with > Nagle+delayed ack kicking in, since the apps eventually end up sending > a very small packets (2 bytes). > We have a case open against Microsoft but since everything is moving > very slow we would like to work around by picking socket buffers that > are multiple of 4k.
Thanks for the patch. One question: > Change log: > 2014-11-18 Iuliu Rus <rus.iu...@gmail.com> > > * net.cc Change default values for socket buffers to fix performance > on 10Gb networks. > > Index: winsup/cygwin/net.cc > =================================================================== > RCS file: /cvs/src/src/winsup/cygwin/net.cc,v > retrieving revision 1.320 > diff -u -p -r1.320 net.cc > --- winsup/cygwin/net.cc 13 Oct 2014 08:18:18 -0000 1.320 > +++ winsup/cygwin/net.cc 18 Nov 2014 19:12:00 -0000 > @@ -621,13 +621,16 @@ fdsock (cygheap_fdmanip& fd, const devic > this is no problem on 64 bit. So we set the default buffer size to > the default values in current 3.x Linux versions. > > - (*) Maximum normal TCP window size. Coincidence? */ > + (*) Maximum normal TCP window size. Coincidence? > + > + NOTE 3. Setting the window size to 65535 results in extremely > bad performance for apps that send data in multiples of Kb, as they > eventually end up sending 1 byte on the network and naggle + delay ack > kicks in. For example, iperf on a 10Gb network gives only 10 Mbits/sec > with a 65535 send buffer. We want this to be a multiple of PAGE_SIZE, > but since 64k breaks WSADuplicateSocket we use 60Kb. We do? See below. > +*/ > #ifdef __x86_64__ > ((fhandler_socket *) fd)->rmem () = 212992; > ((fhandler_socket *) fd)->wmem () = 212992; > #else > - ((fhandler_socket *) fd)->rmem () = 65535; > - ((fhandler_socket *) fd)->wmem () = 65535; > + ((fhandler_socket *) fd)->rmem () = 63488; > + ((fhandler_socket *) fd)->wmem () = 63488; This is 62K, certainly not a multiple of the native PAGE_SIZE of 4K. And this makes me wonder. Did you intend to use 60K and ended up with 62K for a reason? And then, why not 63K as a multiple of 1K? Corinna -- Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Maintainer cygwin AT cygwin DOT com Red Hat
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