Frequent pauses with Linux-based router

[Sean C. Farley]

On Mon, 17 Mar 2008, Bruce M. Simpson wrote:

> Sean C. Farley wrote:
>> I have noticed that with a Linux-based Netgear DG834G (DSL modem)
>> frequent pauses (example[1]) between external systems and 7-STABLE
>> (March 14th).  At first, I thought it was ipfilter or ipnat, but I
>> took those out of the picture by activating telnet on the router and
>> connecting directly to it.  Even running "ls /usr/sbin" on the router
>> would pause occasionally.  I did not (or did not recall) have these
>> problems with 6-STABLE (post 6.2).  I switched out the NIC (FA-311
>> (sis) to a FA-310 (dc)), cable and tried different ports on the modem
>> by which to connect.  I also tried disabling all RFC sysctl's and
>> SACK.  Nothing helped.
>> 
>> Finally, I brought out an old DSL modem (SpeedStream 5660).  This
>> fixed the issue.  I think this maybe a specific issue between Linux
>> (2.4.17_mvl21-malta-mips_fp_le) and FreeBSD 7.  Is there anything
>> else I may test to see what is happening?
>
> OT: Hang on, are you saying you're running a MIPS MALTA targeted Linux
> kernel on a Netgear DG834G? That would be interesting as a test
> platform for FreeBSD/mips, considering the platform support for Malta
> is already there. I had a go at doing the Broadcom Sentry5 SoC last
> year but hadn't finished anything.

Here is a bit of information about it from /proc:
# cat cpuinfo 
processor               : 0
cpu model               : MIPS 4KEc V4.8
BogoMIPS                : 211.35
wait instruction        : no
microsecond timers      : yes
extra interrupt vector  : yes
hardware watchpoint     : yes
VCED exceptions         : not available
VCEI exceptions         : not available

# cat meminfo
         total:    used:    free:  shared: buffers:  cached:
Mem:  14712832  9666560  5046272        0  1130496  3694592
Swap:        0        0        0

If I was not using it for my main DSL router, I would consider putting
FreeBSD on it.  After the frustration I had with it, I did seriously
wonder about FreeBSD on it.  It would be especially tempting if it would
still function as a DSL router along with the web interface.  :)  It has
wireless, but I have that disabled.  If you are interested in more
specs, I can cat /proc for you.

> Long shot, but are 802.3 pause frames appearing anywhere, ie can you
> test with a crossover cable?
> Have you done a BER test with UDP or something like that to try to
> rule out non-TCP protocols?

Well, with help on IRC from Robert Watson and others, I was able to
"fix" it.  An ICMP test showed that there were occasional pauses and
packet loss.  The fix:  use 100Mb instead of 10Mb.  :)  For some reason
I do not recall, I had forced the interface connected to the DSL router
to 10Mb.  When I noticed XP did not have the same problem and that it
had a 100Mb connection to the router, I found and removed the "media
10baseT/UTP mediaopt full-duplex" from /etc/rc.conf for the interface.
That appears to have fixed it.

I have never heard of pause frames.  Interesting.  Also, I do not recall
seeing anything unusual with tcpdump (using "host dsl" expression I
think).  The pause always seemed to be for packets from the router to
the computer.

Sean
-- 
scf at FreeBSD.org