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Awful peformance of DEC500 (Tulip) cards with switches

we've just noticed that the performance of DEC500 Tulip cards running under
RH6.1 (2.2.14 kernel) is pretty awful.
Basically we are getting ~140K Bytes/s (1.4e+02) through a 100TX switch when
doing point-point ftp transfers and network boots are failing. The switch we are
using is an Intel Express 460T.

The strange thing is that using the same nodes and cables and connecting them to
a simple 100TX hub we get 11000 K Bytes/s (1.1e+04)
We also have 3com 100TX cards in these nodes and we have found that we can
achieve 7900 K bytes/s (7.9e+03) when they are connected to the Intel switch.

The switch is reporting large numbers of errors on the ports connected to the
Tulip cards; mostly Fragment errors (Frames which are less than 64-bytes and/or
frames without a start-of-frame). But there are also CRC errors (valid length
frames > 64 bytes which have an FCS error)
I have also observed poor performance when connecting the Tulip cards to a 3com
Super Stack switch.

So my guess is that the Tulip device driver is generating bad frames that are
being ignored by hubs but are being dropped by switches. Has anyone else
observed this behaviour ? Is there a fix ?


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