On Wed, Dec 11, 2019 at 12:12 PM Jonathan Morton <[email protected]> wrote: > > > On 11 Dec, 2019, at 9:54 pm, Dave Taht <[email protected]> wrote: > > > > The DC folk want a multibit more immediate signal, for which L4S is > > kind of targetted, (and SCE also > > applies). I haven't seen any data on how well dctcp or SCE -style can > > work on wildly RTT varying links as yet, although it's been pitched at > > the LTE direction, not at wifi. > > It turns out that a Codel marking strategy for SCE, with modified parameters > of course, works well for tolerating bursty and aggregating links. The > RED-ramp and step-function strategies do not - and they're equally bad if the > same test scenario is applied to DCTCP or TCP Prague.
That matches my preliminary observations. thx. > > The difference is not small; switching from RED to Codel improves goodput > from 1/8th to 80% of nominal link capacity, when a rough model of wifi > characteristics is inserted into our usual Internet-path scenario. While I'm the author of the netem slotting code that does this bursty wifi emulation, and delighted you are using it, it would better to additionally use the delay distribution modelling feature added shortly therafter by members of the stadia team. The distributions of wifi delay with just slotting did not resemble the real world enough for my taste after I fiddled with it extensively. There is a very, very long tail. (or conversely: making wifi retry algos match a sane model better would be good - it makes no sense to have 30 dumb retries in the mac layer! mac retries really dominate my pdv data at these vastly lower levels of queuing) I would love it if google were to publish the wifi distribution tables they have developed since then for inclusion in iproute2. > > We're currently exploring how best to set the extra set of Codel parameters > involved. One of my thoughts after reading about the abc idea is that there is an underused 4th state, in taking away both ect(1) and ect(0) on a previously marked ect(0) stream as a sign you could accellerate. This would only work if you were the only bottleneck router, of course, and not with tcp as we know it. I really like the idea of paced chirping in genera, as it could better fill a wifi aggregate, and perhaps mitigate some of the exponential overshoot problems in slow start (and this is separate from fiddling with abc or other abc states) > - Jonathan Morton > -- Make Music, Not War Dave Täht CTO, TekLibre, LLC http://www.teklibre.com Tel: 1-831-435-0729 _______________________________________________ Bloat mailing list [email protected] https://lists.bufferbloat.net/listinfo/bloat
