netdev - Re: inter-qdisc communication?

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Date:   Fri, 26 Aug 2022 17:06:32 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Thorsten Glaser <t.glaser@...ent.de>
Cc:     netdev@...r.kernel.org
Subject: Re: inter-qdisc communication?

On Fri, 26 Aug 2022 21:34:47 +0200 (CEST) Thorsten Glaser wrote:
> Hi,
> 
> is it possible for qdiscs to communicate with each other?
> 
> For example, if I have a normal egress qdisc and an ingress
> qdisc, how could I “share” configuration values so that e.g.
> a “tc change” can affect both in one run?
> 
> Use case: we have a normal egress qdisc that does a lot of
> things. Now we add artificial latency, and we need to do that
> on ingress as well, for symmetry, obviously, so I’ll write a
> small qdisc that does just that for ingress. But we’re already
> firing a “tc change” to the egress qdisc every few ms or so,
> and I don’t want to double that overhead.

How do you add latency on ingress? 🤔 
The ingress qdisc is just a stub to hook classifiers/actions.