Mt7621 ethernet performance below expectations [SOLVED] – Installing and Using OpenWrt

I have conducted some iperf3 tests on my Netgear R6700v2 (mt7621) device and have noticed that it can only sink packets at ~500Mb/s and source them at around 700Mb/s. I have employed irqbalance and ensured that the iperf3 process is on its own core. There is no NAT involved – packets are going directly do/from the device over hard-line gigabit ethernet. While iperf3 is running, htop shows sirq is ~25%, and the iperf3 process is maxed at 100% on one core.

The interesting thing, is that the same device with DD-WRT installed will source/sink packets at the full link speed, topping out at 950Mb/s (max gigabit speed when overhead is considered) in both directions. In that case, sirq was around 13% and the iperf3 process itself maxed at about 25% CPU usage on one core. Performance was so good, I used this device as the packet source/sink for NAT speed trials for other devices. Double the speed at a fraction of the CPU usage.

I did attempt to activate both software and hardware flow offloading. As expected, since NAT isn’t involved, neither had any effect.

Both DD-WRT and OpenWrt are using the same mt7621 drivers. Any hints at how to improve performance?

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