[dpdk-dev] l2fwd/l3fwd performance drop of about 25% ?

[Richardson, Bruce]

> Hi all,
> 
> I have a quick question regarding the performance of DPDK l2fwd (Same
> problem with l3fwd). I am seeing that when we start multiple ports (e.g.,
> 12 ports), for 64 byte packets, the RX rate is only at around 11 Mpps per
> port, instead of 14.88 Mpps which is the line rate (with preablem+start of
> delimeter + interframe gap). Do you know what could be the problem? I am
> describing my experiment setup below.

When using both ports on a dual-port 10G NIC, you cannot hit line rate on both ports with 64-byte packets due to a lack of PCI bandwidth (for PCI Gen2 x8). If you try with two ports on different NICs you should be getting better performance, as traffic for small packets for a single port at  10G can be handled by the PCI slot. With larger packet sizes, e.g. 128 byte packets, the issue also goes away and the NICs can manage full line rate.