On Wed, Oct 28, 2020 at 11:31:58PM +0100, Tobias Waldekranz wrote:

The thing is, unlike L2 where the hardware will add new neighbors to
its FDB autonomously, every entry in the hardware FIB is under the
strict control of the CPU. So I think you can avoid much of this
headache simply by determining if a given L3 nexthop/neighbor is
"foreign" to the switch or not, and then just skip offloading for
those entries.

You miss out on the hardware acceleration of replacing the L2 header
of course. But my guess would be that once you have payed the tax of
receiving the buffer via the NIC driver, allocated an skb, and called
netif_rx() etc. the routing operation will be a rounding error. At
least on smaller devices where the FIB is typically quite small.

Right, but in that case, there is less of an argument to have something
like DSA injecting directly into an upper device's RX path, if only
mv88e6xxx with bonding is ever going to use that.