[lug] NIC Speed

[Tkil]

>>>>> "svq" == Stephen Queen <svq at peakpeak.com> writes:

svq> I would find it very acceptable to transfer a 100 MB file in
svq> around 26.6 sec [~4MB/s].  It has been my experience that this is
svq> the kind of performance you can expect from a network.

as you point out, there are a huge number of factors involved in
network transfer speed; the capabilities of the NIC make a difference,
but there are many other factors (software TCP/IP stack, most of the
time; data source/sink; hub or switch; wiring quality; traffic).  as
just one example, i found my transfer rates off the athlon box to
improve from 5.5MBps to 7.0MBps on the second and subsequent transfers
of a particular file -- i presume that 1.5MBps difference was due to
reading it off disk vs. having it in ram cache.

i do believe that there is some amount of "you get what you pay for".
Donald Becker characterized the RTL8139 (maybe only the 8129?) as a
"connectivity solution, not a performance solution" [1].  as i'd
consider him one of the 3-4 most knowledgeable people on linux
networking performance, i'd tend to trust his judgement.  (as my
little experiment showed, however, even this "connectivity solution"
showed 6-7MBps without any particular effort on my part.)

having said that, my experiences with the HP-rebranded 3com NICs was
pretty positive -- that's what i saw that 11MBps transfer rate on.  i
also think highly of the tulip chips; towards the end of their life,
you could get them on netgear tx310 (301?) cards for about 20 USD
each, with great support under linux.

so, as with most hardware/system-effect issues, there's no simple
answer.  if your current setup meets your needs, then there's nothing
to fix.  if you find yourself needing more speed, investigate ways to
try to improve your current speed: make sure you're using a switch,
not a hub (experiment with direct-connect crossover cables to elimin-
ate the hub/switch as a factor).  check your connections to see that
they're at the maximum rate supported by the hardware (e.g., 100Mbps
full duplex over cat5 with appropriate NICs).  eventually you should
be able to see much more than 30% of the rated speed of your network.

good luck,
t.

[1] see http://www.scyld.com/network/rtl8139.html, under the section
    "Driver Operation and Comments".