netdev - Re: [RFC PATCH 4/4] net: dsa: tag_edsa: support reception of packets from lag devices

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Date:   Thu, 29 Oct 2020 01:08:58 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Tobias Waldekranz <tobias@...dekranz.com>
Cc:     andrew@...n.ch, vivien.didelot@...il.com, f.fainelli@...il.com,
        netdev@...r.kernel.org, Ido Schimmel <idosch@...sch.org>
Subject: Re: [RFC PATCH 4/4] net: dsa: tag_edsa: support reception of packets
 from lag devices

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.