[Bloat] No backpressure "shaper"+AQM

[Dave Taht]

On Tue, Jul 24, 2018 at 2:31 PM Dave Taht <dave.taht at gmail.com> wrote:
>
> I'd actually written some code for this way back when, if you want to
> know how policers currently work,
> google for "tri-color policer". They worked ok in the T1 era, but suck
> rocks now.
>
> TL;DR
>
> Earlier this week while we (ended up) debugging a buggy comcast modem
> I was desparate enough to resume thinking it was time to revisit the
> concept as a first stage filter prior to hitting cake.
>
> I did think that an *aqm* that aimed for defeating a burst policer
> rate (much like BBR is doing now) would be a goodness. Say you know
> there is a policer upstream configured like yours...
>
> Then... I thought we could build something lighter weight than
> shaping, but the feature set built and built... A few useful
> enhancements to the standard policer like deficits rather than tbf,
> adding ECN, shooting equally at all flows it sees (fq), not shooting
> at one flow for more than one packet in 4 (thus, voip suffers not),
> trying to wait an RTT before shooting again (codel - actually pie in
> this case).

I don't want this convo to die on details. Having a less cpu intensive
than shaping yet more effective than policing "thing" would be a
goodness.

> As one example I controlled the shooting schedule with a 2048 bit, (2
> bits per flow) bitmap sampling every 5ms, keeping around 16 versions
> (thus 80ms of history)

Another variant was bloom filters. I'd played with murmur as an
alternate hash simply because this pull request was a gas:
https://github.com/bitly/dablooms/pull/19

> I discarded the idea for several other reasons back then
>
> ENOFUNDING
> TBF Policers generally are used in switches and routers that do it in
> hardware. Everything I came up with
> was doable in HW (O1) (which cake/fq_codel are not), but waiting 10
> years for it to show up in ISP hardware seemed harder than waiting 10
> years to see ISP shapers get fixed.
> Shaping, given the growing amounts of multi-core underutilized cpus,
> allowed us to be more gentle and achieve
> goals like better e2e host and flow fq, while allowing sparse flows to
> not be delayed very much.
> ENOFUNDING
> Identifying flows required taking a hash which slows things down.
>
> Still, a "slightly better" bobbie aqm influenced policer has long
> seemed doable so long as it's extremely lightweight.



-- 

Dave Täht
CEO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-669-226-2619