[Cake] tossing acks into the background queue

Dave Taht dave.taht at gmail.com
Tue Nov 23 10:12:55 EST 2021

On Tue, Nov 23, 2021 at 2:39 AM Toke Høiland-Jørgensen <toke at toke.dk> wrote:
> Sebastian Moeller <moeller0 at gmx.de> writes:
> > Hi Dave,
> >
> > On 23 November 2021 08:32:06 CET, Dave Taht <dave.taht at gmail.com> wrote:
> >>The context of my question is basically this:
> >>
> >>Is cake baked? Is it done?
> >
> > How about per MAC address fairness (useful for ISPs and to treat
> > IPv4/6 equally)?
> >
> > How about configurable number of queues (again helpful for ISPs)?
> FWIW I don't think CAKE is the right thing for ISPs, except in a
> deployment where there's a single CAKE instance per customer. For
> anything else (i.e., a single shaper that handles multiple customers),
> you really need hierarchical policy enforcement like in a traditional
> HTB configuration. And retrofitting this on top of CAKE is going to
> conflict with the existing functionality, so it probably has to be a
> separate qdisc anyway.

What progress has been made on breaking the HTB locks in the last few years?

Given the enormous number of hw tx/rx queues we see today (64+ on
10gbit), trying to charge off
bandwidth per queue in a cake-derived shaper and protecting the merge
with rcu seemed plausible...

> > IMHO cake works pretty well, with the biggest issue being its CPU
> > demands. As far as I understand however, that is caused by the shaper
> > component and there low latency and throughput are in direct
> > competition, if we want to lower the CPU latency demands we need to
> > allow for bigger buffers that keep the link busy even if cake itself
> > is not scheduled as precisely as we would desire or as e.g. BQL
> > requires.
> Yes, as link speed increases, batching needs to increase to keep up.
> This does not *have* to impact latency, as the faster link should keep
> the granularity constant in the time domain. So experimenting with doing
> this dynamically in CAKE might be worthwhile, but probably not trivial.
> And either way, CAKE is still going to be limited by being single core
> only, and fixing that requires some serious surgery that I seem to
> recall looking into and giving up at some point :(

It was so long ago I don't remember what other issues came up at the time.


I am seeing nvidia offloading red and htb.

> -Toke

I tried to build a better future, a few times:

Dave Täht CEO, TekLibre, LLC

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