Benchmarking Codel and FQ Codel

Please see the complete Best practices for benchmarking Codel and FQ Codel page for extensive details.

Benchmark tool issues

Benchmarks such as netperf,, and netanalyzer are all flawed in that they tend to test single stream behavior, rather than multi-stream. Most of the web based tests peak out at 20Mbits, and none run long enough to generate a statistically valid result.

The core bufferbloat benchmarks all test “latency under load”, for multiple streams. The kind of testing you should do while optimizing your network connection would be, for example, A test, WHILE doing a ping. A netperf, WHILE making a phone call, trying to hold the latency and jitter of the smaller stream (ping or voip)small.

We have developed the Flent tool suite to make benchmarking these various network attributes easier, with results that can be easily shared and graphed several dozen ways. It is available for Linux, BSD, and BSD-derived systems such as OSX.


The codel algorithm uses buffering as a “shock absorber”, and thus, short term udp flooding tests such as netalyzer, show the actual physical amount of buffering, not the amount codel eventually converges on for a single stream. So netanalyzer in particular, will show you have excessive buffering, when a better test would be measuring latency of a second stream.

Unmeasured by anything, fq_codel gives the first packet in each stream priority, so that small streams jump to the front of the queue, allowing for much higher parallelization and utilization. We keep hoping to be able to benchmark this effect on web applications in particular, but haven’t come up with a way to do so.

The fq_codel version of codel won the accolades of codel’s co-designer, Van Jacobson :

fq_codel provides great isolation… if you’ve got low-rate videoconferencing and low rate web traffic they never get dropped. A lot of the issues with iw10 go away, because all that other traffic sees is the front of the queue and you don’t know how big its window is and you don’t care because you are not affected by it. And: fq_codel increases utilization across your entire networking fabric especially for bidirectional traffic… If we’re sticking code into boxes to deploy codel, don’t do that. Deploy fq_codel. It’s just an across the board win.” - Van Jacobson

And since then, we’ve been working on deploying it, rather than refining it.

Third party benchmarks

fq_codel and pie vs cable

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Bufferbloat Related Projects

OpenWrt Project
Congestion Control Blog
Flent Network Test Suite
The Cake shaper
CeroWrt (where it all started)

Network Performance Related Resources

Jim Gettys' Blog - The chairman of the Fjord
Toke's Blog - Karlstad University's work on bloat
Voip Users Conference - Weekly Videoconference mostly about voip
Candelatech - A wifi testing company that "gets it".