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

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Message-ID: <87v7kj597f.fsf@toke.dk>
Date: Mon, 13 Oct 2025 13:31:48 +0200
From: Toke Høiland-Jørgensen <toke@...e.dk>
To: Jamal Hadi Salim <jhs@...atatu.com>
Cc: 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>, Jonas Köppeler
 <j.koeppeler@...berlin.de>, cake@...ts.bufferbloat.net,
 netdev@...r.kernel.org
Subject: Re: [PATCH RFC net-next 0/4] Multi-queue aware sch_cake

Jamal Hadi Salim <jhs@...atatu.com> writes:

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

Thanks!

> Q: Does Eric's riddance of busylock help?

Good question! Probably not for cake_mq usage itself, but maybe it'll
change the baseline? We'll test this before sending a non-RFC :)

-Toke