[Cake] Thinking about ingress shaping & cake
kevin at darbyshire-bryant.me.uk
Sun Apr 12 04:23:42 EDT 2020
> On 10 Apr 2020, at 15:14, Jonathan Morton <chromatix99 at gmail.com> wrote:
> No. If the dequeue rate is never less than the enqueue rate, then the backlog remains at zero pretty much all the time. There are some short-term effects which can result in transient queuing of a small number of packets, but these will all drain out promptly.
> For Cake to actually gain control of the bottleneck queue, it needs to *become* the bottleneck - which, when downstream of the nominal bottleneck, can only be achieved by shaping to a slower rate. I would try 79Mbit for your case.
> - Jonathan Morton
Thanks for correcting my erroneous thinking Jonathan! As I was typing it I was thinking “how does that actually work?” I should have thought more. I typically run ingress rate as 97.5% of modem sync rate (78000 of 80000) which is gives me a little wiggle room when the modem doesn’t quite make the 80000 target (often 79500ish). Egress is easy, 99.5% of 20000 ie. 19900, all is wonderful.
I’m wondering what the relationship between actual incoming rate vs shaped rate and latency peaks is? My brain can’t compute that but I suspect is related to the rtt of the flow/s and hence how quickly the signalling manages to control the incoming rate.
I guess ultimately we’re dependent on the upstream (ISP) shaper configuration, ie if that’s a large buffer and we’ve an unresponsive flow incoming then no matter what we do, we’re stuffed, that flow will fill the buffer & induce latency on other flows.
gpg: 012C ACB2 28C6 C53E 9775 9123 B3A2 389B 9DE2 334A
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