[Cake] Cake in mac80211

Bjørn Ivar Teigen bjorn at domos.no
Wed Feb 5 06:53:14 EST 2020

Thanks for the feedback!

Some comments and questions added inline.

On Tue, 4 Feb 2020 at 18:07, Dave Taht <dave.taht at gmail.com> wrote:

> On Tue, Feb 4, 2020 at 7:25 AM Jonathan Morton <chromatix99 at gmail.com>
> wrote:
> >
> > > On 4 Feb, 2020, at 5:20 pm, Bjørn Ivar Teigen <bjorn at domos.no> wrote:
> > >
> > > Are there any plans, work or just comments on the idea of implementing
> cake in mac80211 as was done with fq_codel?
> >
> > To consider doing that, there'd have to be a concrete benefit to doing
> so.
> Research is research! :) Everything is worth trying! There's got to be
> some better ideas out there, and we have a long list of things we
> could have done to keep improving wifi had funding not run out.
> We barely scratched the surface of this list.
> https://docs.google.com/document/d/1Se36svYE1Uzpppe1HWnEyat_sAGghB3kE285LElJBW4/edit
> > Most of Cake's most useful features, beyond what fq_codel already
> supports, are actually implied or even done better by the WiFi environment
> and the mac80211 layer adaptation (particularly airtime fairness).
> In my opinion(s)
> A) I think ack-filtering will help somewhat on 802.11n, but it's not
> worth the added cpu cost on an AP and I'd prefer hosts reduce their
> ack load in the tcp stack (IMHO, others may differ, it's worth trying)
> B) The underlying wifi scheduler essentially does per host fq better
> than cake can (because it's layer 2 vs layer 3), as per jonathan's
> comment above

C) Instead of using a 8 way set associative hash and 1024 queues,
> fq_codel for wifi uses 4096 with a disambiguation pointer for
> collisions. Seems good enough.

Didn't catch that before. Are the extra queues there because of the
different access categories on Wi-Fi? Seems like that would mean most of
them are not in use considering how little traffic is marked with DSCP.

D) "cobalt" is proving out better in several respects than pure codel,
> and folding in some of that makes sense, except I don't know which
> things are the most valuable considering wifi's other problems

Reading paper now. Thanks for the pointer.

> E) I'd like to dynamically increase the quantum size as a function of
> load or number of flows.

> I'd really like benchmarks of the proprietary versions coming out.
> Qualcomm has their own fq_codelish thing baked into their firmware
> now... I have no idea what broadcom is doing... fq-pie?

I've started looking at benchmarking proprietary drivers with emphasis on
queueing performance. If you have any tips, or if you would like to
co-author a paper (I'm working on a PhD), I am very interested.

> The librerouter is now available. I'd like to try that.
> Recently I benchmarked red rock cafe in mountain view, which had the
> best bufferbloat and rrul score of any cybercafe I'd ever tried - they
> have a mojo networks AP, which arista bought a while back. It was
> lovely.... I have no idea what they do,
> but whatever it was it was *good*. I'm really happy see bufferbloat
> getting fixes everywhere, but really need to add quic to the benchmark
> suite somehow in order to feel better about people not rewriring tcp
> headers to do what they want.
> more importantly:
> Would really like to get cracking on a wifi 6 version. So far, all the
> vendors are lying, there is no OFDMA support in anything we've played
> with. There are some new outer limits there (1000+ devices), a need to
> do gang scheduling, and per-station firmware, and I'm
> profoundly unimpressed with proprietary vendor's efforts so far and
> wish they'd open up their firmware more so more of us could take a
> crack at it....

I agree, there are some interesting problems arising there. Interested to
follow the work if and when this happens. Any luck finding a company
willing to work on open-source drivers for Wi-Fi 6?

> I'd really like to get the intel  (iwl) version, especially the ax200
> chips, ported over to the AQL + fq_codel interfaces, at least.  The
> first attempt went badly, last quarter. Needs eyeballs and time...
> Would like to find some other wifi chip worth fixing - raspi 4? Some
> android wifi chip? what?
> Don't know how the ath11k effort is going...
> In mainline...
>  I'd like to get the wifi codel target on 5ghz down from 20ms (too
> much) to 10ms, (or as I run it here to 8ms) in mainline, or at least
> openwrt, but that would require some benchmarking by multiple folk,
> and I was waiting for the ath10k ATF code to go upstream first. At
> least make it tunable.

Have done some testing myself and 10ms looks like the correct limit on 5GHz.

> Overall, reducing hw retries to sanity would be a nice thing to
> attempt in the ath9k, at least. Although the ongoing SCE work (gradual
> rate reduction) is interesting, I tend to think reducing hardware
> retries (with increased loss) would have a more dramatic effect on
> reducing wifi latencies.
> Presently with the codel target of 20ms in both directions, I get
> 60-80ms tcp latencies (still better than most fiber!) over wifi with a
> 20ms target at 70mbits. What happens at 300+, no idea. cynically I
> think much of the internet is essentially running at a max rwind or
> swind rather than within athe sawtooth.

Also interesting

> doing something more sane to rate limit multicast would be good also.
> It was quite the long list in that google document, back in the day we
> thought the wifi industry might decide to collaborate in order to meet
> the 5G threat.
> > a Cake instance to the wifi interface as well, if you have a need to do
> so.
> It certainly is feasible to do that. I do that now on several 802.11ac
> devices that don't have the fq_codel for wifi hooks, preferring to
> rate limit them well below capacity so as to ensure consistent low
> latency. It's really neat to see people able to play world of warcraft
> and other games over
> the wifi here. ( started deploying ubnt's uap mesh products, reflashed
> with openwrt, along portions of my wifi backbone . Looking forward to
> the AQL backport for those, but I hope someone else does it)

Have this setup at home and it really does make a difference, even with
just normal browsing. Has bigger impact than I would have guessed!

> >
> >  - Jonathan Morton
> > _______________________________________________
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> > Cake at lists.bufferbloat.net
> > https://lists.bufferbloat.net/listinfo/cake
> --
> Make Music, Not War
> Dave Täht
> CTO, TekLibre, LLC
> http://www.teklibre.com
> Tel: 1-831-435-0729

Bjørn Ivar Teigen
Head of Research
Domos, Machine Learning for the Home
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