Performance of CX7 with 'eth' pattern versus 'eth/ipv4' in hairpin

[Tony Hart]

I'm using a CX7 and testing hairpin queues.  The test traffic is
entirely IPv4+UDP with distributed SIP,DIP pairs and received packets
are u-turned via hairpin in the CX7 (single 400G interface).

I see different performance when I use a pattern of 'eth' versus
'eth/ipv4' in the hairpin flow entry.  From testing it seems that
specifying just 'eth' is sufficient to invoke RSS and 'eth/ipv4'
should be equivalent since the traffic is all ipv4, but I'm getting
~104Gbps for the 'eth' pattern and  ~124Gbps for 'eth/ipv4' pattern.

Any thoughts on why there is such a performance difference here?

thanks
tony

This is the 'eth' pattern testpmd commands
flow create 0 ingress group 0 pattern end actions jump group 1 / end
flow create 0 ingress group 1 pattern eth / end actions count / rss
queues 6 7 8 9 end / end

The testpmd commands for 'eth/ipv4'
flow create 0 ingress group 0 pattern end actions jump group 1 / end
flow create 0 ingress group 1 pattern eth / ipv4 / end actions count /
rss queues 6 7 8 9 end / end


This is the testpmd command line...
dpdk-testpmd -l8-14 -a81:00.0,dv_flow_en=1 -- -i --nb-cores 6 --rxq 6
--txq 6 --port-topology loop --forward-mode=rxonly --hairpinq 4
--hairpin-mode 0x10

Versions
mlnx-ofa_kernel-24.04-OFED.24.04.0.6.6.1.rhel9u4.x86_64
kmod-mlnx-ofa_kernel-24.04-OFED.24.04.0.6.6.1.rhel9u4.x86_64
mlnx-ofa_kernel-devel-24.04-OFED.24.04.0.6.6.1.rhel9u4.x86_64
ofed-scripts-24.04-OFED.24.04.0.6.6.x86_64

DPDK: v24.03