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

[Eric Dumazet]

On Wed, 2012-05-16 at 10:17 +0200, Eric Dumazet wrote:
> 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

Actually there is a bug in fq_codel :

The backlog used in codel_should_drop() should not be the flow backlog,
but qdisc backlog, since its more in the codel spirit (allowing a packet
to pass the congestion point regardless of its sojourn_time if the
current queue size is very small)

I'll send a patch to fix this.