netdev - Re: [Cake] [PATCH net-next] net_sched: sch

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Message-ID: <CAA93jw4chUsQ40LQStvJBeOEENydbv58gOWz8y7fFPJkATa9tA@mail.gmail.com>
Date: Mon, 9 Dec 2024 16:25:01 -0800
From: Dave Taht <dave.taht@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Toke Høiland-Jørgensen <toke@...hat.com>, 
	Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org, 
	Jamal Hadi Salim <jhs@...atatu.com>, cake@...ts.bufferbloat.net, 
	Eric Dumazet <edumazet@...gle.com>, Simon Horman <horms@...nel.org>, 
	Cong Wang <xiyou.wangcong@...il.com>, Paolo Abeni <pabeni@...hat.com>, 
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [Cake] [PATCH net-next] net_sched: sch_cake: Add drop reasons

On Mon, Dec 9, 2024 at 3:52 PM Jakub Kicinski via Cake
<cake@...ts.bufferbloat.net> wrote:
>
> On Mon, 09 Dec 2024 13:02:18 +0100 Toke Høiland-Jørgensen wrote:
> > Add three qdisc-specific drop reasons for sch_cake:
> >
> >  1) SKB_DROP_REASON_CAKE_CONGESTED
> >     Whenever a packet is dropped by the CAKE AQM algorithm because
> >     congestion is detected.
> >
> >  2) SKB_DROP_REASON_CAKE_FLOOD
> >     Whenever a packet is dropped by the flood protection part of the
> >     CAKE AQM algorithm (BLUE).
> >
> >  3) SKB_DROP_REASON_CAKE_OVERLIMIT
> >     Whenever the total queue limit for a CAKE instance is exceeded and a
> >     packet is dropped to make room.
>
> Eric's patch was adding fairly FQ-specific reasons, other than flood
> this seems like generic AQM stuff, no? From a very quick look the
> congestion looks like fairly standard AQM, overlimit is also typical
> for qdics?

While I initially agreed with making this generic, preserving the qdisc from
where the drop came lets you safely inspect the cb block (timestamp, etc),
format of which varies by qdisc. You also get insight as to which
qdisc was dropping.

Downside is we'll end up with SKB_DROP_REASON_XXX_OVERLIMIT for
each of the qdiscs. Etc.

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> Cake@...ts.bufferbloat.net
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-- 
Dave Täht CSO, LibreQos