Re: [Make-wifi-fast] Where is the bloat in WiFi?

[Michael Welzl <michawe@ifi.uio.no>]

Thanks a lot - just the info I was looking for  (also from others who have responded in the meantime, thanks!)


> On 6 Oct 2020, at 14:44, Toke Høiland-Jørgensen <toke@toke.dk> wrote:
> 
> Michael Welzl <michawe@ifi.uio.no> writes:
> 
>> Hi, and thanks for a quick answer!
>> 
>> But, it's not quite what I was looking for.... see below:
>> 
>>> On 6 Oct 2020, at 13:47, Toke Høiland-Jørgensen <toke@toke.dk> wrote:
>>> 
>>> Michael Welzl <michawe@ifi.uio.no> writes:
>>> 
>>>> Hi all,
>>>> 
>>>> A simple question to y'all who spent so much time on Cake and things
>>>> ... in a household using WiFi, which buffer is usually bloated? Where
>>>> does the latency really come from?
>>>> 
>>>> Is it:
>>>> 1. the access point's downlink queue, feeding into the WiFi network,
>>> 
>>> This we mostly fixed, but only if you're on a recent OpenWrt with the
>>> right WiFi drivers.
>> 
>> Well okay... I was curious about where the bottleneck is. I can
>> translate my question into: "if Cake is installed everywhere, where
>> does it have the most work to do?".
> 
> Well, CAKE only runs on the upstream link, so that's where it does its
> work. The software shaper model doesn't really work that well on WiFi,
> so we generally encourage people to just run fixed drivers there
> instead. That being said I have heard of one or two WiFi deployments
> where that was not an option, and where CAKE was used as a shaper
> instead. This was for a fixed WiFi backhaul, though, and even so they
> had to set the shaper quite a lot lower than the max bandwidth to get
> reliable performance.
> 
>>> Otherwise, this is a major source of latency *if*
>>> the WiFi link is faster than the downlink from the internet.
>> 
>> Huh? Slower, you mean?
> 
> No, if the WiFi link is faster, the upstream link becomes the bottleneck
> and CAKE has work to do :)
> 
>>> This
>>> depends on both the internet connection and the current rate each WiFi
>>> station operates at, so it can vary wildly, and on very short time
>>> scales.
>> 
>> Sure... I was asking for the "if" in your statement above - since this
>> is an operationally-oriented list: what do people see? What is the
>> more common case?
> 
> Right, well as you can probably tell that might not have been entirely
> clear from your initial post ;)
> 
>>> The extent to which this happens depends on where you are in the
>>> world; personally I've been bottlenecked on the WiFi link ever since
>>> I got a fibre upstream (and with 802.11ax rates maxing at >1Gbps,
>>> maybe that'll change again?).
>> 
>> THIS is what I was after :) one data point, cool - so far, so good...
> 
> Ah, you're after anecdotes - well why didn't you say so? ;)
> 
> In that case I'll add that my own connection is the only one I've come
> across where the WiFi link is *never* the bottleneck. In Denmark we are
> finally (slowly) getting out of the dark ages as far as fibre
> deployments are concerned, but most operators will sell connections
> capped at 100Mbps or 250Mbps, which is still less than the throughout of
> a 802.11ac link with good signal conditions (my phone consistently gets
> ~250-350 Mbps on a speedtest.net run).
> 
> DSL connections tend to have awful latency, and are still quite common,
> but they are pretty easy to fix with CAKE. Cable connections likewise,
> or so is my impression (those are not so common around these parts).
> 
> The worst are definitely LTE/mobile broadband connections. Wildly
> varying link speeds, and awful over-buffering; so you really have to
> clamp them down to get anything useful out of CAKE.
> 
> -Toke