netdev - Re: [PATCH net-next v2 3/6] net: sched: RED: Introduce an ECN tail-dropping mode

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Date:   Wed, 11 Mar 2020 11:36:30 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Petr Machata <petrm@...lanox.com>, netdev@...r.kernel.org
Cc:     Jakub Kicinski <kuba@...nel.org>, Roman Mashak <mrv@...atatu.com>,
        jhs@...atatu.com, xiyou.wangcong@...il.com, davem@...emloft.net,
        jiri@...lanox.com, mlxsw@...lanox.com
Subject: Re: [PATCH net-next v2 3/6] net: sched: RED: Introduce an ECN
 tail-dropping mode



On 3/11/20 10:33 AM, Petr Machata wrote:
> When the RED Qdisc is currently configured to enable ECN, the RED algorithm
> is used to decide whether a certain SKB should be marked. If that SKB is
> not ECN-capable, it is early-dropped.
> 
> It is also possible to keep all traffic in the queue, and just mark the
> ECN-capable subset of it, as appropriate under the RED algorithm. Some
> switches support this mode, and some installations make use of it.
> 
> To that end, add a new RED flag, TC_RED_TAILDROP. When the Qdisc is
> configured with this flag, non-ECT traffic is enqueued (and tail-dropped
> when the queue size is exhausted) instead of being early-dropped.
> 

I find the naming of the feature very confusing.

When enabling this new feature, we no longer drop packets
that could not be CE marked.

Tail drop is already in the packet scheduler, you want to disable it.


How this feature has been named elsewhere ???
(you mentioned in your cover letter : 
"Some switches support this mode, and some installations make use of it.")