netdev - Re: [RFC PATCH v2 net-next 04/10] net: bridge: switchdev: allow the data plane forwarding to be offloaded

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Date:   Mon, 12 Jul 2021 13:03:23 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Tobias Waldekranz <tobias@...dekranz.com>
CC:     Grygorii Strashko <grygorii.strashko@...com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Ido Schimmel <idosch@...sch.org>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <nikolay@...dia.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        "bridge@...ts.linux-foundation.org" 
        <bridge@...ts.linux-foundation.org>,
        Alexander Duyck <alexander.duyck@...il.com>
Subject: Re: [RFC PATCH v2 net-next 04/10] net: bridge: switchdev: allow the
 data plane forwarding to be offloaded

On Mon, Jul 12, 2021 at 02:28:42PM +0200, Tobias Waldekranz wrote:
> > After cutting my teeth myself with Tobias' patches, I tend to agree with
> > the idea that the macvlan offload framework is not a great fit for the
> > software bridge data plane TX offloading. Some reasons:
>
> I agree. I was trying to find an API that would not require adding new
> .ndos or other infrastructure. You can see in my original RFC cover that
> this was something I wrestled with.
>
> > - the sb_dev pointer is necessary for macvlan because you can have
> >   multiple macvlan uppers and you need to know which one this packet
> >   came from. Whereas in the case of a bridge, any given switchdev net
> >   device can have a single bridge upper. So a single bit per skb,
> >   possibly even skb->offload_fwd_mark, could be used to encode this bit
> >   of information: please look up your FDB for this packet and
> >   forward/replicate it accordingly.
>
> In fact, in the version I was about to publish, I reused
> skb->offload_fwd_mark to encode precisely this property. It works really
> well. Maybe I should just publish it, even with the issues regarding
> mv88e6xxx. Let me know if you want to take a look at it.

I am on it already, I have a 25-patch series that is currently
undergoing testing (yes, it changes all switchdev drivers to call
switchdev_bridge_port_offload() and switchdev_bridge_port_unoffload(),
and it also moves the switchdev object replay helpers to push mode, and
only then it hooks a "bool tx_fwd_offload" argument to the
switchdev_bridge_port_offload() call).
If all goes well and I still have some time today I will publish it for
review. Naturally the final submissions, when net-next reopens, will be
in much smaller chunks.