weird network problems on current since 10/28/2012

[Manfred Antar]

At 03:21 AM 11/4/2012, 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 at 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?

I read the commit log and tried that. It didn't change.
I will try the patch from Andre and enable the debug log.
Manfred

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