From:   Kurt Kanzenbach <kurt@linutronix.de>
To:     Vladimir Oltean <vladimir.oltean@nxp.com>
Cc:     netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Jamal Hadi Salim <jhs@mojatatu.com>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        Jiri Pirko <jiri@resnulli.us>,
        Vinicius Costa Gomes <vinicius.gomes@intel.com>,
        Gerhard Engleder <gerhard@engleder-embedded.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next 3/3] net/sched: taprio: dynamic max_sdu larger
 than the max_mtu is unlimited
In-Reply-To: <20230216102914.wat37qsih5xx3wk4@skbuf>
References: <20230215224632.2532685-1-vladimir.oltean@nxp.com>
 <20230215224632.2532685-4-vladimir.oltean@nxp.com> <87cz6aot67.fsf@kurt>
 <20230216102914.wat37qsih5xx3wk4@skbuf>
Date:   Thu, 16 Feb 2023 11:34:33 +0100
Message-ID: <875yc1q4p2.fsf@kurt>
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On Thu Feb 16 2023, Vladimir Oltean wrote:
> On Thu, Feb 16, 2023 at 10:28:48AM +0100, Kurt Kanzenbach wrote:
>> On Thu Feb 16 2023, Vladimir Oltean wrote:
>> > It makes no sense to keep randomly large max_sdu values, especially if
>> > larger than the device's max_mtu. These are visible in "tc qdisc show".
>> > Such a max_sdu is practically unlimited and will cause no packets for
>> > that traffic class to be dropped on enqueue.
>> >
>> > Just set max_sdu_dynamic to U32_MAX, which in the logic below causes
>> > taprio to save a max_frm_len of U32_MAX and a max_sdu presented to user
>> > space of 0 (unlimited).
>> >
>> > Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
>>=20
>> Doesn't this deserve a Fixes tag as well?
>
> No, I don't think so. It's just so that the user (and later, the offloadi=
ng
> driver) doesn't see arbitrarily large values, just a simplifying 0.

Yes, exactly. It's visible by the user.

> I guess it could potentially make a difference to the software taprio
> data path with TSO, if the max MTU is comparable with the segment
> sizes.
>
> Anyway, with or without the Fixes tag, the patch lands in the same place.

Yup. It doesn't really matter that much.

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

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