[Cake] cake default target is too low for bbr?
xnoreq at gmail.com
Fri Apr 28 17:11:36 EDT 2017
As I understand it, increase in RTT due to queueing of packets is the
main feedback mechanism for BBR.
So dropping packets, which I already consider harmful, is really harmful
with BBR because you're not telling the sender to slow down.
Instead, with a controlled delay qdisc like cake or codel, you're
telling the sender to keep sending the data faster because the qdisc
keeps the increase in RTT minimal. To make things worse, you're throwing
away perfectly good packets with no effect other than wasting bandwidth.
I'm not sure how BBR handles jitter or how small of an increase in RTT
it detects as "congestion" but from my limited testing, I've noticed no
problems with steam downloads in the bulk tin with 15 ms target in cake.
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