[Bloat] No backpressure "shaper"+AQM

[Jonathan Morton]

> On 24 Jul, 2018, at 11:11 pm, Benjamin Cronce <bcronce at gmail.com> wrote:
> 
> The problem that I'm getting is by adding my own shaping, a measurable amount of the benefit of their AQM is lost. While I am limited to Codel, HFSC+Codel, or FairQ+Codel for now, I am actually doing a worse job of anti-bufferbloat than my ISP is. Fewer latency spices according to DSLReports.

We do know that applying SQM at the entry to the bottleneck link works much better than at the exit.  It's a fundamental principle.

> That's when I thought of a backpressure-less AQM. Instead of having backpressure and measuring sojourn time as a function of how long it takes packets to get scheduled, predict an estimated sojourn time based on the observed rate of flow, but allow packets to immediately vacate the queue. The AQM would either mark ECN or drop the packet, but never delay the packet.

It's a reasonable idea.  The key point is to use a deficit-mode scheduler/shaper, rather than the credit-mode ones that are common (mainly TBF/HTB).  The latter are why you have such a big, uncontrolled burst from the ISP in the first place.

 - Jonathan Morton