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

[Dave Taht]

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.

so:

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
http://www.teklibre.com
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