10BT Full-Duplex problems (still)

Paul S. Graham grahamp@ee.byu.edu
Fri Apr 9 12:38:41 1999

I know I have mentioned this before, but I figured I would ask again
to see if anyone else has had the problem and been able to solve it. I
work in a lab with several machines running Linux.  Of these machines,
8 machines are using the SMC EtherPower II cards (with the epic100
driver) and two use 3Com 905B cards.  The lab also has HP and Sun Unix
machines. The problem that we have is that we would like to run all of
our machines using 10BaseT Full-Duplex, but with the SMC cards there
are some serious transfer rate problems in this mode under Linux.
Under NT/95, these SMC cards get close to 8 or 9 Mb/s throughput in
both full- and half-duplex to any machine.  Under Linux, we get as
much as 6-7 Mb/s throughput out and only about 1 Mb/s throughput in
using full-duplex with the SMC cards when talking to HP-UX boxes.
When talking between a HD and FD Linux machines with SMC cards, data
rates from the FD to the HD machines are about 8 Mb/s while the other
direction they are only 3-4 Mb/s.  At half-duplex, throughput
approaches 8 Mb/s both directions to about any machine from a Linux
box with an SMC card.  We don't see this throughput problem with the
3Com 905B cards at all--both directions and both duplex modes see
about 8 Mb/s throughput rates. We have seen this behavior with the SMC
cards ever since the v0.10 or v1.01 drivers (when we first got the

Further, to see if I could improve NFS performance for Linux, I have
been trying out the 2.2.5 and 2.2.5-ac6 kernels.  I have seen more
than a two-times improvement in NFS write performance with the
2.2.5-ac6 kernel and version 1.07 of the epic100 driver running at
half-duplex.  I saw an improvement in NFS writes under full-duplex,
but the poor data input rates in full-duplex (about .25 Mb/s) to our
HP-UX machines makes things quite irritating.  As a result, I have
been using a half-duplex port and enjoying the better NFS performance.
As you can see, the combination of 1.07 of the epic driver and the
2.2.5-ac6 has made things worse at full-duplex.

Besides switching all of the SMC Linux boxes to half-duplex is there
something else I can do to fix the performance problems?  What things
can I do to debug the operation of the driver?  The problem has been
quite frustrating and I would be willing to put a little time into it
to get everything working nicely.


Paul Graham (grahamp@ee.byu.edu)
459 CB, Electrical Engineering Dept.
Brigham Young University
Provo, Utah 84602
phone: (801)378-7206  fax: (801)378-6586

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