linux-kernel - Re: [PATCH net-next 04/13] net/sched: taprio: allow user input of per-tc max SDU

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Date:   Wed, 14 Sep 2022 23:11:59 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Vinicius Costa Gomes <vinicius.gomes@...el.com>
CC:     "netdev@...r.kernel.org" <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>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>,
        Rui Sousa <rui.sousa@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Michael Walle <michael@...le.cc>,
        Maxim Kochetkov <fido_max@...ox.ru>,
        Colin Foster <colin.foster@...advantage.com>,
        Richie Pearn <richard.pearn@....com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Vladimir Oltean <olteanv@...il.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Gerhard Engleder <gerhard@...leder-embedded.com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 04/13] net/sched: taprio: allow user input of
 per-tc max SDU

On Wed, Sep 14, 2022 at 04:03:26PM -0700, Vinicius Costa Gomes wrote:
> Could you please add an example of the 'tc' command syntax you are
> thinking about?

I was working with this, as a matter of fact:

#!/bin/bash

h1=eno0
h2=eno2
swp1=swp0
swp2=swp4

ip link set $h2 address 00:01:02:03:04:05
ip link set $h1 up
ip link set $h2 up
tc qdisc del dev $swp1 root || :
ip link del br0 || :

ip link add br0 type bridge && ip link set br0 up
ip link set $swp1 master br0 && ip link set $swp1 up
ip link set $swp2 master br0 && ip link set $swp2 up
tc qdisc replace dev $swp1 root taprio \
	num_tc 8 \
	map 0 1 2 3 4 5 6 7 \
	queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 \
	base-time 0 \
	sched-entry S 0x7f 990000 \
	sched-entry S 0x80  10000 \
	max-sdu 0 0 0 0 0 0 0 200 \
	flags 0x2

echo "Run:"
echo "isochron rcv --interface $h1 &"
echo "isochron send --interface $h2 --client 127.0.0.1 --cycle-time 0.001 --frame-size 60 --omit-sync --num-frames 10 --priority 7 --vid 0"

I've also tested it in software mode, and at least on my system, a 10 us
interval is not really enough for the qdisc to make forward progress and
dequeue any packet. My application freezes until I destroy the qdisc and
re-create it using a larger interval for TC7. I'll debug that some more.
I was thinking, after the basic queueMaxSDU feature is merged, maybe
taprio could automatically further limit queueMaxSDU based on the
smallest intervals from the schedule. Something like a generalization of
vsc9959_tas_guard_bands_update(), basically.

> Another point to think about: does it make sense to allow 'only' the
> max-sdu to be changed, i.e. the user doesn't set an a schedule, nor a
> map, only the max-sdu information.

Maybe, I haven't tried. I think iproute2 doesn't currently support
skipping TCA_TAPRIO_ATTR_SCHED_ENTRY_LIST.