On Wed, Mar 18, 2015 at 8:20 AM, Jonathan Morton <chromatix99@gmail.com> wrote:

> On 18 Mar, 2015, at 17:10, Kathleen Nichols <nichols@pollere.com> wrote:
>
> How are you relating target delay to bandwidth?

Essentially, I use 5ms as a minimum, and increase it if necessary to accommodate a couple of MTU-sized packets at the shaping rate.  This keeps things nicely under control at low bandwidths, and I find that cake remains useful and usable even at 64Kbps (without making even the usual adjustments to host or link configuration for such low speeds).

In the cake2 (or maybe it was the unpublished cake3) version, I had a lighter weight version of the codel algorithm, that did not have a target parameter at all. Instead it just took the interval parameter and shifted it 
right 4 (yielding a target of 6.xms from an interval of 100ms)

This saves on a memory access (and storage per queue!) , and I felt that any differences in behavior would be unnoticeable. And they were. This is also above the bound for cable-modem media access that greg white (rightly or wrongly) believed existed. So I have no problem in eliminating "target" entirely.

Cake (without bandwidth shaping engaged) uses more cpu than fq_codel did and this was one of many optimizations I'd attempted (or successfully added). Cake with shaping is a bit less cpu than sqm-scripts htb + fq_codel + filters. 

It also looked like cake could be poured into gates, with a bit more research, and testing.


I can do this in cake because the shaping rate is known, whereas the pure codel and fq_codel qdiscs do not have reliable link-speed information.

As for this bit, we seemed to need to account for a MTU's worth of data at the lower speeds, and I did not explore what fiddling with the interval and auto-calc-ing the target did at these speeds, as yet.
 
- Jonathan Morton

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Let's make wifi fast, less jittery and reliable again!

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