Re: [dpdk-users] Throughput dropping by half with 1B increase in packet size

["Wiles, Keith" <keith.wiles@intel.com>]

> On Feb 9, 2018, at 9:39 AM, Theano <theanosaurus@gmail.com> wrote:
> 
> Hi All,
> 
> We are eventually going to build an application over DPDK, and we've
> started out with a very simple pktgen-like application that sends and
> receives packets to a different machine running l2fwd.
> 
> With packets up to 64B (60B headers and payload + 4B of FCS), l2fwd shows
> line rate packet forwarding of this application's packets. As soon as the
> packet size increases to 65B, the throughput (in pps) halves. With
> dpdk-pktgen we observe a much more graceful decline in packet throughput as
> packet size increases.
> 
> I examined the dpdk-pktgen code and can't find any significant differences
> between how it constructs its packets vs. how we do it, but of course I'm
> missing something.
> 
> Has anyone seen this before and/or has any ideas on how to identify the
> problem?

Adding one byte will push you to have two cache lines used and that can reduce performance. Make sure the packets are aligned to a 64 byte boundary.

Other then that I see no reason for the 1/2 performance without comparing the code. Pktgen-dpdk I spent a fair amount of time looking at the performance, but I also had to play with burst size and the number of packet sent to the NIC they too need to be cached aligned or multiples of a cache line.

> 
> We are using DPDK version 17.02.1; please let me know if any other
> information would be helpful.
> Thanks,
> Theano.

Regards,
Keith