[Cerowrt-devel] happy 4th!

Toke Høiland-Jørgensen toke at toke.dk
Tue Jul 9 03:57:20 EDT 2013

Mikael Abrahamsson <swmike at swm.pp.se> writes:

> For me, it shows that FQ_CODEL indeed affects TCP performance
> negatively for long links, however it looks like the impact is only
> about 20-30%.

As far as I can tell, fq_codel's throughput is about 10% lower on
100mbit in one direction, while being higher in the other. For 10mbit
fq_codel shows higher throughput throughout?

> What's stranger is that latency only goes up to around 230ms from its
> 200ms "floor" with FIFO, I had expected a bigger increase in buffering
> with FIFO. Have you done any TCP tuning?

Not apart from what's in mainline (3.9.9 kernel). The latency-inducing
box is after the bottleneck, though, so perhaps it has something to do
with that? Some interaction between netem and the ethernet link?

> Would it be easy for you to do tests with the streams that "loads up
> the link" being 200ms RTT, and the realtime flows only having 30-40ms
> RTT, simulating downloads from a high RTT server and doing interactive
> things to a more local web server.

Not on my current setup, sorry. Also, I only did these tests because I
happened to be at my lab anyway yesterday. Not going back again for a
while, so further tests are out for the time being, I'm afraid...

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