The MTU of eth0.2 or bat0?
It doesn't matter, I cannot set the MTU of eth0.2, eth0 or eth1 to something higher than 1500
One of the performance penalties might occur when batman-adv needs to use fragmentation. batman-adv is going to add its own header on top of the 1500 byte frames received on bat0.
That's why I'm trying to increase the MTU
1536 on eth0.2 looks good though. Then 1500 bytes should fit without fragmentation on bat0. You can check with "batctl td" or Wireshark if you see batman-adv fragments on eth0.2.
That's only the config. IP LINK still showing 1500.
If 1536 is somehow not applied to eth0.2, might be a driver issue then. You can check wether you can manually alter an interface MTU with "ip link dev eth0.2 set mtu 1536", for instance.
Actual OpenWRT trunk on TP-Link C7 / C2600 devices. Can decrease to anything lower than 1500 but cannot raise above 1500.
Thanks, Andi