[Bloat] when does the CoDel part of fq_codel help in the real world?

[Stephen Hemminger]

On Fri, 30 Nov 2018 06:51:34 +0100 (CET)
Mikael Abrahamsson <swmike at swm.pp.se> wrote:

> On Thu, 29 Nov 2018, Stephen Hemminger wrote:
> 
> > The problem is that any protocol is mostly blind to the underlying 
> > network (and that can change).  To use dave's analogy it is like being 
> > put in the driver seat of a vehicle blind folded.  When you step on the 
> > gas you don't know if it is a dragster, jet fighter, or a soviet 
> > tractor. The only way a protocol can tell is based on the perceived 
> > inertia and when it runs into things...  
> 
> Actually, I've made the argument to IETF TCPM that this is not true. You 
> can be able to communicate earlier data from previous flows on the same 
> connection so that new flows can re-learn this.
> 
> If no flow the past hour has been able to run faster than 1 megabit/s and 
> always PMTUD to 1460 bytes MTU outbound, then there is good chance that 
> the next flow will encounter the same thing. Why not use this information 
> when guessing how things will behave going forward?
> 

Since a majority of the flows in the world are coming from mobile, this both
makes sense but is hard.  Linux used to remember TCP metrics but this was
removed with the flow cache.