netdev - switchdev offload & ecmp

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Date:   Mon, 15 May 2017 16:25:43 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Jiri Pirko <jiri@...nulli.us>, Ido Schimmel <idosch@...lanox.com>
Cc:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        netdev <netdev@...r.kernel.org>
Subject: switchdev offload & ecmp

Hi Jiri and Ido,

I'm trying to understand how ecmp offloading works. It seems that rocker doesn't
support it:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/ethernet/rocker/rocker_ofdpa.c#n2409.
But I saw that the support was added in spectrum:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/?h=684a95c064fc.

Is there a consistency between the ecmp algorithm of the kernel and the one from
spectrum?
I suspect that there can be scenarii where some packets of a flow are forwarded
by the driver and some other are forwarded by the kernel.
For example, an ecmp route with two nexthops: a connected route and a gw? In
that case, the periodic nexthops update
(https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c#n987)
won't help. How do you ensure that all packets of the flow are always forwarded
through the same nexthop?

Regards,
Nicolas