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

[Eric Dumazet]

On Wed, 2012-05-16 at 12:59 +0300, Jonathan Morton wrote:
> That's a pretty specific type of blackhole - one that can pass enough
> ECN information to permit negotiation of an ECN flow, but which then
> squashes Congestion Experienced codepoints. How common are those?
> 

Very common since TCP ECN negociation doesnt use ECN on IP header.

(SYN, SYNACK, and ACK messages dont use ECT)

So a network playing games with TOS field can be a ECN blackhole, still
allowing TCP to negociate ECN enabled sessions.

> If fq_codel drops from the head of the longest flow when the queue is
> physically full, rather than the next one to be serviced, all should
> be well even in that case. 

Not really. Unless you afford 3 second delay in queue.