netdev - Re: [PATCH v6 net-next 02/13] net/sched: mqprio: refactor offloading and unoffloading to dedicated functions

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Date:   Thu, 16 Feb 2023 15:41:23 +0100
From:   Ferenc Fejes <fejes@....elte.hu>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     peti.antal99@...il.com, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Jacob Keller <jacob.e.keller@...el.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Simon Horman <simon.horman@...igine.com>
Subject: Re: [PATCH v6 net-next 02/13] net/sched: mqprio: refactor
 offloading and unoffloading to dedicated functions

Hi Vladimir!

On Thu, 2023-02-16 at 16:28 +0200, Vladimir Oltean wrote:
> Hi Ferenc,
> 
> On Thu, Feb 16, 2023 at 02:05:22PM +0100, Ferenc Fejes wrote:
> > This patch just code refactoring or it modifies the default
> > behavior of
> > the offloading too? I'm asking it in regards of the veth interface.
> > When you configure mqprio, the "hw" parameter is mandatory. By
> > default,
> > it tries to configure it with "hw 1". However as a result, veth
> > spit
> > back "Invalid argument" error (before your patches). Same happens
> > after
> > this patch too, right?
> 
> Yup. iproute2 has a default queue configuration built in, if nothing
> else is specified, and this has "hw 1":
> https://git.kernel.org/pub/scm/network/iproute2/iproute2.git/tree/tc/q_mqprio.c#n36
> 
> > For veth hardware offloading makes no sense, but giving the "hw 0"
> > argument explicitly as mqprio parameter might counterintuitive.
> 
> Agree that giving the right nlattrs to mqprio and trying to slalom
> through their validation is a frustrating minesweeper game. I have
> some
> patches which add some netlink EXT_ACK messages to make this a bit
> less
> sour. I'm regression-testing those, together with some other mqprio
> changes and I hope to send them soon.

Nice, good to hear!

> 
> OTOH, "hw 1" is mandatory with the "mode", "shaper", "min_rate" and
> "max_rate" options. This is logical when you think about it (driver
> has
> to act upon them), but indeed it makes mqprio difficult to configure.
> 
> With veth, you need to use multi-queue to make use of mqprio/taprio,
> have you done that?
> 
> ip link add veth0 numtxqueues 8 numrxqueues 8 type veth peer name
> veth1

Yes, usually I done it with ethtool --set-channels veth0 tx 8 but I
guess that both resulting the same.

Best,
Ferenc