Hardware Flow Offloading and PPPoE: not working?

Hi folks! Sorry for posting (maybe) on the wrong category.

I'm running 21.02 stable on a Mikrotik RB750 gr3 (MT7621 based), connected to a GPON internet with PPPoE.

On LAN side I have a dedicated host running Iperf3, connected by ethernet cable to Mikrotik.

On WAN side there are two interfaces on the same ethernet port: a PPPoE interface, that uses my GPON internet to connect to the World, and a local IP address (192.168.15.2). A simple Port Forward firewall rule redirects external 5201 port (on any WAN address) to the LAN dedicated Iperf3 host.

I've made two set of tests with Iperf3, all of them without any SQM / QoS.

First set (Hardware Flow Offloading ENABLED):

  • test 1: from a host on internet, connecting to my global PPPoE IP address on port 5201. It uses aprox. 35% of sirq CPU (number obtained from "top" running on the Mikrotik).

  • test 2: from a host on "local WAN network" (IP 192.168.15.3), connecting to 192.168.15.2 on port 5201. Uses 1% of sirq CPU. 920Mbits of bandwidth.

Second set (Hardware Flow Offloading DISABLED):

  • test 1: same behavior of test 1.

  • test 2: uses 50% of sirq CPU, speed was dropped by a factor of two.

From this observation it seems that Hardware Flow Offloading is working fine but not for PPPoE.

My GPON is today a 360Mbits down / 160Mbits up link. It seems that the MT7621 cores are enough for this internet speed range, observed from Iperf3 results from Test 1 on both sets. But my expectation is to upgrade this speed to >600Mbits in a year timeframe, and I thing that those cores will not be enough.

I've made a test with 19.07 and Hardware Flow Offloading was working as expected for PPPoE too, for a couple of hours (until it crashes the whole device, a known bug and a major reason to upgrade to 21.02 that brings stability on this functionality).

My understand of Hardware Flow Offloading not working for PPPoE proceed? There is any configuration needed for my case? Should I upgrade to Development builds?

If any configuration file is needed to understand my tests I can send it.

Cheers!

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