[Make-wifi-fast] Higher latency on upload under poor signal conditions

[Sebastian Moeller]

Hi Michael,


> On Jun 16, 2020, at 12:18, Michael Yartys via Make-wifi-fast <make-wifi-fast at lists.bufferbloat.net> wrote:
> 
> 
> From: Michael Yartys <michael.yartys at protonmail.com>
> Subject: Higher latency on upload under poor signal conditions
> Date: June 16, 2020 at 12:18:38 GMT+2
> To: "make-wifi-fast at lists.bufferbloat.net" <make-wifi-fast at lists.bufferbloat.net>
> Reply-To: Michael Yartys <michael.yartys at protonmail.com>
> 
> 
> Hi
> 
> I decided to run some 8-stream TCP tests at the edge of the range of my WiFi network, and I noticed that I get higher latency when I run an upload compared to a download. The latency when downloading is pretty steady at right above 30 ms, and when I run the upload it hovers around 80-100 ms. I think I know why this happens, but I would like to read the opinion of the mailing list.

	My naive guess would be that air-time fairness by the AP only directly affects the AP's own transmissions, the stations will in all likelihood not have an fq_codel instance in its wifi-stack (I could be wrong, but I do not believe that the 7260ac intel card actually uses airtime fairness yet/at all). So the 80-100ms might just come from the default wifi parameters which typically are adjusted for peak thoughput instead of a balanced throughput latency under load set-point. Then again that is my _guess_, so Kruger-Dunning might apply.

Best Regards
	Sebastian


> 
> My test setup is a NETGEAR R7800 running OpenWrt with fq_codel'd WiFi and a laptop with an Intel 7260 ac wireless card. The laptop reports an average signal strength of about -77 dBm, while the router has a much harder time hearing the laptop at -98 dBm signal strength with a noise floor of -109 dBm.
> 
> I suspect this extra latency is due to buffering because the laptop has to retransmit a lot of frames due to how poorly the router hears it. Is this correct?
> 
> The associated flent files are attached.
> 
> Michael
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