[Bloat] Thoughts on Stochastic Fair Blue

[Juliusz Chroboczek]

Sorry for the delay, but I wanted to think this over.

> My second observation is that marking and dropping both happen at the
> tail of the queue, not the head.  This delays the congestion information
> reaching the receiver, and from there to the sender, by the length of
> the queue

It's very difficult to drop at the head of the queue in SFB, since we'd
need to find a suitable packet that's in the same flow.  Since SFB makes
heroic efforts to keep the queue size small, this shouldn't make much of
the difference.

Your suggestion is most certainly valid for plain BLUE.

> Another observation is that packets are not re-ordered by SFB, which
> (given the Bloom filter) is potentially a missed opportunity.

What's your suggestion?

> However, they can be re-ordered in the current implementation by
> using child qdiscs such as SFQ

I don't see how that buys you anything.  SFB is very aggressive with
dropping packets when under congestion, and the packet drop happens
*before* the child qdisc gets a chance to see the packet; hance, putting
SFQ below SFB won't buy you much, it'll just reorder packets in the
small queue that SFB allows.  Or am I missing something?

-- Juliusz