[Codel] [Bloat] Exploring the potential of codel, fq_codel, and qfq

[Eric Dumazet]

On Wed, 2012-05-16 at 09:47 +0200, Eric Dumazet wrote:

> On TCP_RR pure workload, you have one packet in flight per flow.
> 
> ECN adds nothing in this case, only that no 'drops' occurs at all.
> 
> It might be good to change fq_codel to perform ECN mark only if flow
> queue has more packets.
> 
> If not, plain drop.

And for codel, if all packets are ECN enabled, there is no 'drop' on a
pure TCP_RR workload, you endup codel downgraded to pfifo

An idea would be following :

If sojourn_time is above a new limit (say ecn_threshold), drop packet no
matter it is ECN capable or not.

This still gives incentive to ECN flows, but allow drops in case all
flows are ECN.

target = 5ms ;
ecn_threshold = target * 2;
interval = 100ms;