Date: Sun, 4 Nov 2012 07:16:01 -0500 From: Kim Culhan <w8hdkim@gmail.com> To: Dimitry Andric <dimitry@andric.com> Cc: Adrian Chadd <adrian@freebsd.org>, freebsd-current@freebsd.org, Andre Oppermann <andre@freebsd.org> Subject: Re: weird network problems on current since 10/28/2012 Message-ID: <CAKZxVQVzCeiwvQ1KVntmyEQxhYEN5E-qZzYkOU1psT537x%2Bjsw@mail.gmail.com>
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On Sun, November 4, 2012 6:21 am, Dimitry Andric wrote: > On 2012-11-04 02:13, Manfred Antar wrote: >> At 03:29 PM 11/3/2012, Adrian Chadd wrote: >>> On 3 November 2012 10:40, Manfred Antar <null@pozo.com> wrote: >>>> i have problem connecting to freebsd box on local network since last sunday. >>>> the last kernel that works: >>>> FreeBSD 10.0-CURRENT #0: Sun Oct 28 12:14:38 PDT 2012 >>>> anything after that, sometimes i can connect, other times just hangs. >>>> any network connection hangs ===== pop httpd ssh etc etc. >>>> anyone have any ideas ? >>>> i can checkout different sources and see if i can locate the changes that cause >>>> this. >>> >>> Please do! > ... >> Here is what I found doing : >> setenv CVSROOT /usr/home/ncvs >> >> cvs co -D"October 28, 2012 12:14:38 PDT" sys >> >> A kernel from that time works fine. >> >> doing: >> >> cvs up -D"October 28, 2012 13:14:38 PDT" sys 1 hour later >> the following files were changed: >> sys/netinet/tcp_input.c >> sys/netinet/tcp_timer.c >> sys/netinet/tcp_var.h >> >> Building a kernel from these new files is when the problem starts. > > So, your problems seem to have been introduced by this commit by Andre: > > http://svn.freebsd.org/changeset/base/242266 > > Increase the initial CWND to 10 segments as defined in IETF TCPM > draft-ietf-tcpm-initcwnd-05. It explains why the increased initial > window improves the overall performance of many web services without > risking congestion collapse. > > As long as it remains a draft it is placed under a sysctl marking it > as experimental: > net.inet.tcp.experimental.initcwnd10 = 1 > When it becomes an official RFC soon the sysctl will be changed to > the RFC number and moved to net.inet.tcp. > > This implementation differs from the RFC draft in that it is a bit > more conservative in the case of packet loss on SYN or SYN|ACK because > we haven't reduced the default RTO to 1 second yet. Also the restart > window isn't yet increased as allowed. Both will be adjusted with > upcoming changes. > > Is is enabled by default. In Linux it is enabled since kernel 3.0. > > After the commit, there was a small discussion thread on svn-src-head@ > about the possible problems with the approach. Maybe you are > experiencing those? > > As the commit message says, you should be able to turn the feature off > using: > > sysctl net.inet.tcp.experimental.initcwnd10=0 > > Can you please try that, and see if the problems go away? FWIW this did not make the problem go away here. thanks -kim --
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