Bad LAN performance from router to PC (AR9132+AR9344)

I have two routers running OpenWRT 19.07.2

Today out of curiosity if my routers would still make sense with a better WAN contract, I measured performance by using iperf in both directions with shocking results.

Router -> PC ~75Mbit/s (!!)
PC -> Router ~220Mbit/s

The PC was connected with 1000MBit Ethernet. I could live with far less than this, but 75Mbit/s are unexpected. I also connected a different PC and it did not help. Both were running recent kernels.

Can anyone confirm?
Hardware used:

system type             : Atheros AR9132 rev 2
machine                 : Buffalo WZR-HP-G300NH

system type             : Atheros AR9344 rev 2
machine                 : NETGEAR WNDR3700v4

Are you running iperf on the benchmarked device?

For a real test it should be:
pc (iperf) <-> router <-> another pc (iperf)

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Yes, I did that on the device.

Sorry for my stupid post, I see that the CPU core is pretty much maxed out by iperf3.

I will test NAT WAN/LAN performance with a second pc on the wan port then as soon as I am able to.

Thanks for the reply, and sorry for the noise

No problem, you're welcome.

Between two PCs, the hardware switch does the work, and you should get basically line speed.

To answer the question "What ISP speed can this router handle?" you should set up a PC as a simulated ISP (on a different subnet) and connect it to the WAN port, and iperf to it from a PC on the LAN network. This will test how fast the router CPU can route and NAT.

I did a real life test on the AR9344 using a real 250MBit/s WAN. With NAT offloading on.

No Problem for OpenWRT to handle full 250MBit/s with 60% idle.

I did not realize that pushing packets from userspace on the router itself is so slow. That was why my initial test was completley crap to get any idea of NAT performance.

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