[Cake] [PATCH net-next 0/4] Multi-queue aware sch_cake

["Toke Høiland-Jørgensen" <toke@redhat.com>]

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.

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.

---
Changes since RFC:

- Drop the sync_time parameter for now and always use the 200 us value.
  We are planning to explore auto-configuration of the sync time, so
  this is to avoid committing to a UAPI. If needed, a parameter can be
  added back later.
- Keep the tc yaml spec in sync with the new stats member
- Rebase on net-next
- Link to RFC: https://lore.kernel.org/r/20250924-mq-cake-sub-qdisc-v1-0-43a060d1112a@redhat.com

---
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

 Documentation/netlink/specs/tc.yaml |   3 +
 include/uapi/linux/pkt_sched.h      |   1 +
 net/sched/sch_cake.c                | 619 +++++++++++++++++++++++++++++-------
 3 files changed, 500 insertions(+), 123 deletions(-)
---
base-commit: e05021a829b834fecbd42b173e55382416571b2c
change-id: 20250902-mq-cake-sub-qdisc-cdf0b59d2fe5