[LEDE-DEV] [PATCH] ar71xx: Add GRO support to ag71xx

[Felix Fietkau]

On 2017-09-03 20:35, Rosen Penev wrote:
> On a TL-WN710N, this patch increases iperf performance from ~92.5 to ~93.5 mbps.> Keep in mind the WN710N is a 100mbps device. I expect greater numbers
from gigabit devices.
> 
> Signed-off-by: Rosen Penev <rosenp at gmail.com>
Hi Rosen,

Sorry about that, but I will have to revert this change. It causes a
serious regression in LAN->WAN routing performance on various devices.
I did some digging and found out why:
For GRO to work properly, checksums of incoming packets have to be
verified very early in the network stack. The Ethernet MAC does not
support rx checksum offload, so this has to happen in software.
Due to the very small cache size, this causes a significant increase in
memory bus traffic.
It might be possible in the future to avoid this by making use of the
checksum offload engine, but that's a separate component on the chip and
not present on every SoC (only the newer ones).
It also requires a significant rework of the Ethernet driver, which I
don't have any time for.

- Felix