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

[Vladimir Oltean]

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.