[Bloat] [Bug 1436945] Re: devel: consider fq_codel as the default qdisc for networking

[Jonathan Morton]

> On 5 Jun, 2018, at 9:34 pm, Sebastian Moeller <moeller0 at gmx.de> wrote:
> 
> The rationale for that decision still is valid, at low bandwidth every opportunity to send a packet matters…

Yes, which is why the DRR++ algorithm is used to carefully choose which flow to send a packet from.

> …and every packet being transferred will increase the queued packets delay by its serialization delay.

This is trivially true, but has no effect whatsoever on inter-flow induced latency, only intra-flow delay, which is already managed adequately well by an ECN-aware sender.

May I remind you that Cake never drops the last packet in a flow subqueue due to AQM action, but may still apply an ECN mark to it.  That's because dropping a tail packet carries a risk of incurring an RTO before retransmission occurs, rather than "only" an RTT delay.  Both RTO and RTT are always greater than the serialisation delay of a single packet.

Which is why ECN remains valuable even on very low-bandwidth links.

 - Jonathan Morton