netdev - Re: [PATCH net-next 0/2] net: stmmac: add EthType Rx Frame steering

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Message-ID: <20211210113821.522b7c00@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Fri, 10 Dec 2021 11:38:21 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Ong Boon Leong <boon.leong.ong@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Jose Abreu <joabreu@...opsys.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        alexandre.torgue@...s.st.com,
        Kurt Kanzenbach <kurt.kanzenbach@...utronix.de>,
        netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org,
        Amritha Nambiar <amritha.nambiar@...el.com>
Subject: Re: [PATCH net-next 0/2] net: stmmac: add EthType Rx Frame steering

On Fri, 10 Dec 2021 13:57:30 +0200 Vladimir Oltean wrote:
> Is it the canonical approach to perform flow steering via tc-flower hw_tc,
> as opposed to ethtool --config-nfc? My understanding from reading the
> documentation is that tc-flower hw_tc only selects the hardware traffic
> class for a packet, and that this has to do with prioritization
> (although the concept in itself is a bit ill-defined as far as I
> understand it, how does it relate to things like offloaded skbedit priority?).
> But selecting a traffic class, in itself, doesn't (directly or
> necessarily) select a ring per se, as ethtool does? Just like ethtool
> doesn't select packet priority, just RX queue. When the RX queue
> priority is configurable (see the "snps,priority" device tree property
> in stmmac_mtl_setup) and more RX queues have the same priority, I'm not
> sure what hw_tc is supposed to do in terms of RX queue selection?

You didn't mention the mqprio, but I think that's the piece that maps
TCs to queue pairs. You can have multiple queues in a TC.

Obviously that's still pretty weird what the flow rules should select
is an RSS context. mqprio is a qdisc, which means Tx, not Rx.

Adding Amritha who I believe added the concept of selecting Rx queues
via hw_tc. Can you comment?