[Cake] [PATCH net-next v6] Add Common Applications Kept Enhanced (cake) qdisc

Dave Taht dave.taht at gmail.com
Mon Apr 30 17:27:44 EDT 2018

On Mon, Apr 30, 2018 at 2:21 PM, Cong Wang <xiyou.wangcong at gmail.com> wrote:
> On Sun, Apr 29, 2018 at 2:34 PM, Toke Høiland-Jørgensen <toke at toke.dk> wrote:
>> sch_cake targets the home router use case and is intended to squeeze the
>> most bandwidth and latency out of even the slowest ISP links and routers,
>> while presenting an API simple enough that even an ISP can configure it.
>> Example of use on a cable ISP uplink:
>> tc qdisc add dev eth0 cake bandwidth 20Mbit nat docsis ack-filter
>> To shape a cable download link (ifb and tc-mirred setup elided)
>> tc qdisc add dev ifb0 cake bandwidth 200mbit nat docsis ingress wash
>> CAKE is filled with:
>> * A hybrid Codel/Blue AQM algorithm, "Cobalt", tied to an FQ_Codel
>>   derived Flow Queuing system, which autoconfigures based on the bandwidth.
>> * A novel "triple-isolate" mode (the default) which balances per-host
>>   and per-flow FQ even through NAT.
>> * An deficit based shaper, that can also be used in an unlimited mode.
>> * 8 way set associative hashing to reduce flow collisions to a minimum.
>> * A reasonable interpretation of various diffserv latency/loss tradeoffs.
>> * Support for zeroing diffserv markings for entering and exiting traffic.
>> * Support for interacting well with Docsis 3.0 shaper framing.
>> * Extensive support for DSL framing types.
>> * Support for ack filtering.
> Why this TCP ACK filtering has to be built into CAKE qdisc rather than
> an independent TC filter? Why other qdisc's can't use it?

I actually have a tc - bpf based ack filter, during the development of
cake's ack-thinner, that I should submit one of these days. It
proved to be of limited use.

Probably the biggest mistake we made is by calling this cake feature a
filter. It isn't.

Maybe we should have called it a "thinner" or something like that? In
order to properly "thin" or "reduce" an ack stream
you have to have a queue to look at and some related state. TC filters
do not operate on queues, qdiscs do. Thus the "ack-filter" here is
deeply embedded into cake's flow isolation and queue structures.

>> * Extensive statistics for measuring, loss, ecn markings, latency
>>   variation.
>> A paper describing the design of CAKE is available at
>> https://arxiv.org/abs/1804.07617
> Thanks.


Dave Täht
CEO, TekLibre, LLC
Tel: 1-669-226-2619

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