netdev - Re: [RFC PATCH net-next 11/15] net/sched: taprio: warn about missing size table

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Message-ID: <87357uvp6j.fsf@kurt>
Date:   Sat, 28 Jan 2023 13:06:28 +0100
From:   Kurt Kanzenbach <kurt@...utronix.de>
To:     Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org
Cc:     Vinicius Costa Gomes <vinicius.gomes@...el.com>
Subject: Re: [RFC PATCH net-next 11/15] net/sched: taprio: warn about
 missing size table

On Sat Jan 28 2023, Vladimir Oltean wrote:
> Vinicius intended taprio to take the L1 overhead into account when
> estimating packet transmission time through user input, specifically
> through the qdisc size table (man tc-stab).
>
> Something like this:
>
> tc qdisc replace dev $eth root stab overhead 24 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 0x7e 9000000 \
> 	sched-entry S 0x82 1000000 \
> 	max-sdu 0 0 0 0 0 0 0 200 \
> 	flags 0x0 clockid CLOCK_TAI
>
> Without the overhead being specified, transmission times will be
> underestimated and will cause late transmissions.
>
> We can't make it mandatory, but we can warn the user with a netlink
> extack.
>
> Link: https://patchwork.kernel.org/project/netdevbpf/patch/20220505160357.298794-1-vladimir.oltean@nxp.com/
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Reviewed-by: Kurt Kanzenbach <kurt@...utronix.de>

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