netdev - [PATCH RFC net-next 0/4] Multi-queue aware sch

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Message-Id: <20250924-mq-cake-sub-qdisc-v1-0-43a060d1112a@redhat.com>
Date: Wed, 24 Sep 2025 14:16:02 +0200
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Toke Høiland-Jørgensen <toke@...e.dk>, 
 Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang <xiyou.wangcong@...il.com>, 
 Jiri Pirko <jiri@...nulli.us>, "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>
Cc: Jonas Köppeler <j.koeppeler@...berlin.de>, 
 cake@...ts.bufferbloat.net, netdev@...r.kernel.org, 
 Toke Høiland-Jørgensen <toke@...hat.com>
Subject: [PATCH RFC net-next 0/4] Multi-queue aware sch_cake

This series adds a multi-queue aware variant of the sch_cake scheduler,
called 'cake_mq'. Using this makes it possible to scale the rate shaper
of sch_cake across multiple CPUs, while still enforcing a single global
rate on the interface.

The approach taken in this patch series is to implement a separate qdisc
called 'cake_mq', which is based on the existing 'mq' qdisc, but differs
in a couple of aspects:

- It will always install a cake instance on each hardware queue (instead
  of using the default qdisc for each queue like 'mq' does).

- The cake instances on the queues will share their configuration, which
  can only be modified through the parent cake_mq instance.

Doing things this way does incur a bit of code duplication (reusing the
'mq' qdisc code), but it simplifies user configuration by centralising
all configuration through the cake_mq qdisc (which also serves as an
obvious way of opting into the multi-queue aware behaviour).

The cake_mq qdisc takes all the same configuration parameters as the
cake qdisc, plus on additional parameter to control the sync time
between the individual cake instances.

We are posting this series to solicit feedback on the API, as well as
wider testing of the multi-core shaper.

An earlier version of this work was presented at this year's Netdevconf:
https://netdevconf.info/0x19/sessions/talk/mq-cake-scaling-software-rate-limiting-across-cpu-cores.html

The patch series is structured as follows:

- Patch 1 factors out the sch_cake configuration variables into a
  separate struct that can be shared between instances.

- Patch 2 adds the basic cake_mq qdisc, based on the mq code

- Patch 3 adds configuration sharing across the cake instances installed
  under cake_mq

- Patch 4 adds the shared shaper state that enables the multi-core rate
  shaping

A patch to iproute2 to make it aware of the cake_mq qdisc is included as
a separate patch as part of this series.

---
Jonas Köppeler (1):
      net/sched: sch_cake: share shaper state across sub-instances of cake_mq

Toke Høiland-Jørgensen (3):
      net/sched: sch_cake: Factor out config variables into separate struct
      net/sched: sch_cake: Add cake_mq qdisc for using cake on mq devices
      net/sched: sch_cake: Share config across cake_mq sub-qdiscs

 include/uapi/linux/pkt_sched.h |   2 +
 net/sched/sch_cake.c           | 635 +++++++++++++++++++++++++++++++++--------
 2 files changed, 514 insertions(+), 123 deletions(-)
---
base-commit: dc1dea796b197aba2c3cae25bfef45f4b3ad46fe
change-id: 20250902-mq-cake-sub-qdisc-cdf0b59d2fe5