Re: [Cake] Cake3 - source code and some questions

[Adrian Popescu <adriannnpopescu@gmail.com>]

That answers my question. Will the changes to codel made by cake be
put into fq_codel?

On Sun, Apr 12, 2015 at 9:57 PM, Jonathan Morton <chromatix99@gmail.com> wrote:
> This is a question worth discussing. There is a certain amount of
> controversy over the actual meaning, utility and constraints of the target
> parameter, although the interval parameter is fairly well understood as a
> rough (order of magnitude) estimate of the prevailing RTT.
>
> Note that even with FTTP, while the RTT to the head end may be unusually
> low, the RTTs to interesting servers will still be in roughly the same range
> as on a good quality ADSL link. This is especially true if the interesting
> servers tend to be at the other end of the country/continent or on the other
> side of an ocean. This variability is within Codel's capacity.
>
> Due to the Diffserv and flow isolation features of cake, the latency
> minimization feature provided by Codel also isn't as critical to tune as it
> is when standalone, or with a lesser flow isolation system such as
> fq_codel's collision prone hash function. I think this is sufficient to make
> further tuning unnecessary up to 1 gigabit, whether on a LAN or over the
> internet, and since I haven't seen any home affordable gear for more than a
> gigabit yet - marketing tricks by Wi-Fi vendors aside - I don't think it's
> worth thinking too hard about pushing that higher in the home use case.
> Fq_codel also works quite well on a LAN already.
>
> The difference in a datacentre is that typical native RTTs are measured in
> microseconds, well outside the range that Codel is by default tuned for. The
> bandwidths involved also mean that the standard 5ms target invokes a large
> amount of buffered data. Additionally, we're inherently talking about a
> wholly local environment, so there is no need to adapt to internet scale
> RTTs.
>
> For those cases where you do have a datacentre like environment connected to
> an internet like environment, the solution is obvious. Deploy datacentre
> tuned AQM (which might be fq_codel with altered parameters) within the
> datacentre, and put cake at the gateway(s) to the internet. Job done.
>
> - Jonathan Morton