[dpdk-dev] Rx-errors with testpmd (only 75% line rate)

[Michael Quicquaro <michael.quicquaro@gmail.com>]

Hello,
My hardware is a Dell PowerEdge R820:
4x Intel Xeon E5-4620 2.20GHz 8 core
16GB RDIMM 1333 MHz Dual Rank, x4 - Quantity 16
Intel X520 DP 10Gb DA/SFP+

So in summary 32 cores @ 2.20GHz and 256GB RAM

... plenty of horsepower.

I've reserved 16 1GB Hugepages

I am configuring only one interface and using testpmd in rx_only mode to
first see if I can receive at line rate.

I am generating traffic on a different system which is running the netmap
pkt-gen program - generating 64 byte packets at close to line rate.

I am only able to receive approx. 75% of line rate and I see the Rx-errors
in the port stats going up proportionally.
I have verified that all receive queues are being used, but strangely
enough, it doesn't matter how many queues more than 2 that I use, the
throughput is the same.  I have verified with 'mpstat -P ALL' that all
specified cores are used.  The utilization of each core is only roughly 25%.

Here is my command line:
testpmd -c 0xffffffff -n 4 -- --nb-ports=1 --coremask=0xfffffffe
--nb-cores=8 --rxd=2048 --txd=2048 --mbcache=512 --burst=512 --rxq=8
--txq=8 --interactive

What can I do to trace down this problem?  It seems very similar to a
thread on this list back in May titled "Best example for showing
throughput?" where no resolution was ever mentioned in the thread.

Thanks for any help.
- Michael