Strange network performance on Intel Rangeley (8 cores Atom)

Olivier Cochard-Labbé olivier at
Mon Mar 3 20:55:16 UTC 2014

Hi all,

I've got a new toy in my network bench lab: a SuperMicro SuperServer
But I've got a problem for understanding and obtaining good throughput for
"routing" or "firewalling" usages.

I'm using only the embedded 4 gigabit ports of the Atom C2758 SoC.
With the default igb(4) parameters which is to create 8 queues (because
there is 8 cores) this server is not able to receive more than 585K
packet-per-seconds into one port which is far from the gigabit line-rate
(1.48Mpps): I was expecting better throughput with 8 cores.
Then I did a bunch of new benchmarks by measuring the impact of number of
queue and the results are here:

=> I've got better results with only 4 queues than 8... but still low
throughput with only 938Kpps.

Then I decided to measure the impact of pf and ipfw on the throughput with
4 and 8 queues.
And the results are annoying:

=> With 8 queues, enabling pf or ipfw improve the input throughput of the
igb(4) port.

Why so low throughput with 8 queues ?
Why better throughput with pf or ipfw enabled than without ?



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