netdev - Re: [PATCH v4 net-next 00/15] Allow forwarding for the software bridge data path to be offloaded to capable devices

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Message-ID: <20210720132026.mpk3iq3z6vmmzxyd@skbuf>
Date:   Tue, 20 Jul 2021 16:20:26 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     Vladimir Oltean <vladimir.oltean@....com>, 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>,
        Tobias Waldekranz <tobias@...dekranz.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <nikolay@...dia.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        bridge@...ts.linux-foundation.org,
        Grygorii Strashko <grygorii.strashko@...com>,
        Marek Behun <kabel@...ckhole.sk>,
        DENG Qingfang <dqfext@...il.com>,
        Vadym Kochan <vkochan@...vell.com>,
        Taras Chornyi <tchornyi@...vell.com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Steen Hegelund <Steen.Hegelund@...rochip.com>,
        UNGLinuxDriver@...rochip.com,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>
Subject: Re: [PATCH v4 net-next 00/15] Allow forwarding for the software
 bridge data path to be offloaded to capable devices

On Tue, Jul 20, 2021 at 02:24:29PM +0300, Ido Schimmel wrote:
> Too many things are squashed into this one patchset. It needs to be
> split.
>
> The TX forwarding offload in mv88e6xxx is not related to the replay
> stuff and should be added in a separate patchset. This can be done by
> first adding the switchdev_bridge_port_offload() /
> switchdev_bridge_port_unoffload() APIs that only take care of setting /
> unsetting the hardware domain for the bridge port. Then, in a different
> patchset, these APIs can be augmented with a parameter for the replay
> stuff. It should be easier to review that way and require less
> unnecessary surgeries in drivers that do not require the added
> functionality.

Fair point. I will submit patches 1-10 and 11-15 separately.

> According to the title, the patchset is focused on improving
> performance, but there are no performance numbers that I could see and
> most of the patches deal with the replay stuff instead.

Maybe, but the truth is that it is not really the performance
improvement that I care about. The performance quote is from Tobias'
original cover letter, which I took as-is. I can build a synthetic test
for multicasting on 10 mv88e6xxx ports or something like that, or maybe
Tobias can provide a more relevant example out of Westermo's use cases.
But it would be silly if this patchset's acceptance would depend on the
numbers. This is one of those cases where completely different interests
led me and Tobias to the the same solution.

I don't want to bore you to death with details, but for some switches
(DSA or otherwise), being able to send bridge packets as they are (data
plane packets) instead of what they aren't (control plane packets) is a
matter of functionality and not performance. Such switches only use
control plane packets for link-local packet traps, and sending/receiving
a control packet is expensive.

For this class of switches (some may call them "dumb", but whatever),
this patch series makes the difference between supporting and not
supporting local IP termination through a VLAN-aware bridge, bridging
with a foreign interface, bridging with software upper interfaces like
LAG, etc.