fxp driver performance expectations

Paul Marciano pm940 at yahoo.com
Thu Jun 15 18:25:42 UTC 2006


I am running FreeBSD-5.4 on a 3GHz P4 with two Intel
fxp NICs running IP forwarding with polling enabled.

For larger packets (e.g. 700 bytes) I am getting
100Mbps throughput port to port.

For min-size packets (64 bytes) I am only seeing
around 60Mbps.  Increasing HZ and the polling
parameters does not help.

I tried a couple of Gigabit Ethernet cards, using the
em driver and they can sustain 100Mbps.

For further comparison I tried a recent Linux install
and got a little over 20Mbps for 64 byte packets.  So
much for that.

Does anyone know if I should be expecting more
performance out of the fxp?  Again, the em NICs work
beyond 100Mbps with min sized frames.

I want to know if there's more performance to be had
from the hardware.  My working assumption is that the
driver is mature, it's a popular NIC, so maybe I'm
getting all there is out of it.  However, if the
driver has been written optimized for larger packets
at the expense of smaller packets, then perhaps
there's work I can do.

The goal, by the way, is to forward min-sized frames
at line rate.  It's a dumb goal, but one that
marketing people care about.

I clearly have no clue here, so please feel free to
give me one.


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