Hi Ben,
Thank you for the suggestions and questions.
We've connected a pair of modern high-performance boxes with integrated
copper Gb/s Intel NICS, with an ethernet crossover cable, and have run some
netperf full duplex TCP tests. The transfer rates are well below wire
speed. We're reporting this as a kernel bug, because we expect a vanilla
kernel with default settings to give wire speed (or close to wire speed)
performance in this case. We DO see wire speed in simplex transfers. The
behavior has been verified on multiple machines with identical hardware.
Try using NICs in the pci-e slots. We have better luck there, as you
usually have more lanes and/or higher quality NIC chipsets available in
this case.
It's a good idea. We can try this, though it will take a little time to
organize.
Try a UDP test to make sure the NIC can actually handle the throughput.
I should have mentioned this in my original post -- we already did this.
We can run UDP wire speed full duplex (over 900 Mb/s in each direction, at
the same time). So the problem stems from TCP or is aggravated by TCP.
It's not a hardware limitation.
Look at the actual link usage as reported by the ethernet driver so that
you take all of the ACKS and other overhead into account.
OK. We'll report on this as soon as possible.
Try the same test using 10G hardware (CX4 NICs are quite affordable
these days, and we drove a 2-port 10G NIC based on the Intel ixgbe
chipset at around 4Gbps on two ports, full duplex, using pktgen). As in
around 16Gbps throughput across the busses. That may also give you an
idea if the bottleneck is hardware or software related.
OK. That will take more time to organize.
Cheers,
Bruce
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