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

[Jamal Hadi Salim <jhs@mojatatu.com>]

On Wed, Sep 24, 2025 at 8:16 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> 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.
>

For this version of the patchset
Reviewed-by: Jamal Hadi Salim <jhs@mojatatu.com>

Q: Does Eric's riddance of busylock help?

cheers,
jamal
> ---
> 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
>