I've got a pair of dual G5s running 2.6.4. For a second gigE link we
added in some Intel 82540EM cards, using the mainline e1000 driver with
NAPI enabled. lspci reports the bus as 66MHz. The cards were connected
together with a crossover cable.
A basic UDP packet-blasting program in userspace using 64KB datagrams
could only manage 47MB/s of data throughput, using 20% of a cpu.
For comparison, the same program managed 108.9 MB/s with 30% cpu when
using the onboard gigE ports.
Also, I tried setting a larger mtu using "ip set link dev ethx mtu
xxxxx". No matter what value I chose (even setting it to its default
value, which should have had zero effect) it resulted in the link not
being able to transfer data. Downing/upping the link didn't clear the
issue, neither did unloading/reloading the driver module. It took a
reboot to actually get it working again.
Any ideas what's going on?
Thanks,
Chris
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