[Ecn-sane] some 100 flow 100Mbit tests of cake, fq_codel, pie, with ecn on or off

Dave Taht dave.taht at gmail.com
Fri Sep 21 14:35:53 EDT 2018

As it happens, I'm primarily trying to get to the root causes of
babeld going flaky on me, and my primary purpose was to test babeld
1.8.3 while under load, but I have a few observations in this dataset.

It is WAY easier if you just download the tarball and use flent to
look at the various graphs.


wget http://flent-fremont.bufferbloat.net/~d/babel-ecn.tgz

or browse: http://flent-fremont.bufferbloat.net/~d/babel-ecn/

I started writing up things, with pictures, and so on, and that
started to get long, and I want to finish blowing babel up (if I can)
before I can safely deploy it so...

The test was client <-> 100Mbit bottleneck <-> server
with ecn on or off on cubic tcp.

I ran most of them at a higher resolution (-s .02). See the included
test script for more details. Running at this resolution required many
minutes and 7GB's of memory to post-process the files.

I need to go fix tc-iterate so I can get queue depths again. I'd also
like to add irtt support to tcp_nup - I'm A) mostly interested in
making babel fail, and B) tcp flows

I did collect a ton of interesting statistics on the tcp flows. The
tcp rtt CDFs, in particular.

The files with no qdisc mentioned are cake.

0) I did the fq_codel_fast tests using memlimit 4M (the openwrt
default, so far as I know(?)

1) At this workload, pie's ecn support gets disabled almost completely
- the drop probability cracks 10% and it drops away... something like
370 packets marked vs 49000 dropped.

* You can see cake doing quite well vis a vis fq_codel, but you can
also see that the RTT is inflated in either case with ecn on vs off.

* You can see the effects of hash collisions on codel - one test had a
major hash collision on the measurement flow.

* Probably the most interesting result (and one reason why I started
fiddling with the bulk dropper code in the first place)

was cake vs fq_codel_fast, attached.

But: DO suck down these files and peruse for yourself.


Dave Täht
CTO, TekLibre, LLC
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