netdev - Re: [PATCH net-next 2/3] net/sched: taprio: don't allow dynamic max

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Date:   Thu, 16 Feb 2023 10:27:57 +0100
From:   Kurt Kanzenbach <kurt@...utronix.de>
To:     Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        Gerhard Engleder <gerhard@...leder-embedded.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 2/3] net/sched: taprio: don't allow dynamic
 max_sdu to go negative after stab adjustment

On Thu Feb 16 2023, Vladimir Oltean wrote:
> The overhead specified in the size table comes from the user. With small
> time intervals (or gates always closed), the overhead can be larger than
> the max interval for that traffic class, and their difference is
> negative.
>
> What we want to happen is for max_sdu_dynamic to have the smallest
> non-zero value possible (1) which means that all packets on that traffic
> class are dropped on enqueue. However, since max_sdu_dynamic is u32, a
> negative is represented as a large value and oversized dropping never
> happens.
>
> Use max_t with int to force a truncation of max_frm_len to no smaller
> than dev->hard_header_len + 1, which in turn makes max_sdu_dynamic no
> smaller than 1.
>
> Fixes: fed87cc6718a ("net/sched: taprio: automatically calculate queueMaxSDU based on TC gate durations")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

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

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