On Tue, 21 Oct 2008 16:36:05 -0700 (PDT)
David Miller [off-list ref] wrote:

From: Jarek Poplawski <redacted>
Date: Fri, 17 Oct 2008 22:12:10 +0200

quoted

pkt_sched: sch_netem: Limit packet re-ordering functionality to tfifo qdisc.

After introducing qdisc->ops->peek() method the only remaining user of
qdisc->ops->requeue() is netem_enqueue() using this for packet
re-ordering. According to Patrick McHardy: "a lot of the functionality
of netem requires the inner tfifo anyways and rate-limiting is usually
done on top of netem. So I would suggest so either hard-wire the tfifo
qdisc or at least make the assumption that inner qdiscs are work-
conserving." This patch tries the former.

Signed-off-by: Jarek Poplawski <redacted>

This is an interesting patch.

But the thing that strikes me is this: Why don't we just let sch_netem do
the reordering inside of itself entirely and just get rid of all of this
->requeue() business?

sch_netem is just a black box, like any other packet scheduler node in
the tree, and so it can internally do the reordering with a self managed
packet list or similar.  All of this can be hidden inside of it's ->dequeue()
with some pkt_sch watchdog timer that fires to prevent stale packets sitting
in the reorder queue forever.

Anyways, just and idea and RFC, just like this patch ;-)

The problem is that jamal talked me into having netem as a classful qdisc,
instead of doing its own rate control.  People like to do use TBF as inner qdisc,
and do reordering.