[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 14:42:47 EDT 2018

On Fri, Sep 21, 2018 at 11:35 AM Dave Taht <dave.taht at gmail.com> wrote:
> 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.

To clarify, the ruler flat line is cake.

The other line is fq_codel and it's collisions.

> But: DO suck down these files and peruse for yourself.
> --
> Dave Täht
> CTO, TekLibre, LLC
> http://www.teklibre.com


Dave Täht
CEO, TekLibre, LLC
Tel: 1-669-226-2619

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