20% packet loss with re0 in gigE mode vs. 0% in 100BT

Sean McNeil sean at mcneil.com
Mon Oct 11 21:16:14 PDT 2004

On Mon, 2004-10-11 at 12:31, Robert Watson wrote:
> On Mon, 11 Oct 2004, Sean McNeil wrote:
> > > Assuming you're not filling the send buffer, it would definitely suggest a
> > > driver, configuration, or hardware bug.  There have recently been a number
> > > of changes to the if_re driver to fix support for jumbo frames, etc.  It
> > > would be interesting to know whether backing out to earlier revisions of
> > > the if_re driver affect the problem you're seeing.  In particular,
> > > ifre.c:1.35 was the jumbo frame change, so 1.34 would be interesting, and
> > > 1.31 is before some other related changes.  Likewise, you could try
> > > backing out to before locking was introduced by setting debug.mpsafenet=0
> > > in loader.conf and then backing out to if_re.c:1.29.  I might be generally
> > > useful to try setting debug.mpsafenet=0 with the current driver to
> > > eliminate that as a possible concern.
> > 
> > These are good suggestions as well, but I have heard from another user
> > that has seen this kind of thing over all of these versions.  It is less
> > likely then that the jumbo or locking changes caused the issue. 
> Have you tried 4.x to see if the same problem occurs there?
> Have you tried the normal juggling of ACPI, APIC, and other configuration
> variables?  It sounds like things work fine at minimal bandwidth rates, so
> that probably rules out interrupt problems and the like, but I figured it
> was worth asking.
> I assume you've probably looked at substituting the switch, forcing
> auto-negotiation to 1gb, etc?

I wrote a small program to look at the data a little.  It looks a lot
like a bursting issue yet the data is metered out and shouldn't have
this kind of problem.  It is an MPEG-2 transport stream.  What I see is
typically I'll get 42 packets through just fine and then 11 packets
lost. The maximum number of packets I get before a drop is 449 and I've
lost a maximum of 51 in a row.  For the most part, though, it is very
close to 42 good then 11 missing.  This is with 928448 total packets and
176591 missing.  Packets are 1316 bytes each.

Again, 100BT has no packet loss.  Only happens with gigE.  It is
possible that my Linksys 8-port gigE switch is dropping them but I find
this highly unlikely.  More likely this has something to do with the
if_re driver and how it does transmit.  It uses a periodic timer.


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