Jakub Kicinski [off-list ref] writes:

On Fri, 10 Jan 2020 11:56:57 +0530, gautamramk@gmail.com wrote:

quoted

From: "Mohit P. Tahiliani" <redacted>

Principles:
  - Packets are classified on flows.
  - This is a Stochastic model (as we use a hash, several flows might
                                be hashed on the same slot)
  - Each flow has a PIE managed queue.
  - Flows are linked onto two (Round Robin) lists,
    so that new flows have priority on old ones.
  - For a given flow, packets are not reordered.
  - Drops during enqueue only.
  - ECN capability is off by default.
  - ECN threshold is at 10% by default.
  - Uses timestamps to calculate queue delay by default.

Usage:
tc qdisc ... fq_pie [ limit PACKETS ] [ flows NUMBER ]
                    [ alpha NUMBER ] [ beta NUMBER ]
                    [ target TIME us ] [ tupdate TIME us ]
                    [ memory_limit BYTES ] [ quantum BYTES ]
                    [ ecnprob PERCENTAGE ] [ [no]ecn ]
                    [ [no]bytemode ] [ [no_]dq_rate_estimator ]

defaults:
  limit: 10240 packets, flows: 1024
  alpha: 1/8, beta : 5/4
  target: 15 ms, tupdate: 15 ms (in jiffies)
  memory_limit: 32 Mb, quantum: device MTU
  ecnprob: 10%, ecn: off
  bytemode: off, dq_rate_estimator: off

Some reviews below, but hopefully someone who knows more about qdiscs
will still review :)

I looked it over, and didn't find anything you hadn't already pointed
out below. It's pretty obvious that this started out as a copy of
sch_fq_codel. Which is good, because that's pretty solid. And bad,
because that means it introduces another almost-identical qdisc without
sharing any of the code...

I think it would be worthwhile to try to consolidate things at some
point. Either by just merging code from fq_{codel,pie}, but another
option would be to express fq_codel and fq_pie using the fq{,_impl}.h
includes. Maybe even sch_cake as well, but that may take a bit more
work. Not sure if we should require this before merging fq_pie, or just
leave it as a possible enhancement for later? WDYT?

-Toke