[Bloat] Curious bufferbloat on DOCSIS connection with many downloads

[Dave Taht]

Power save?

On Tue, Jan 16, 2018 at 11:36 AM, Arie <nospam at ariekanarie.nl> wrote:
> Recently I accidentally discovered something quite odd about my home DOCSIS
> connection (shaped with cake) while running a flent rrul test.
> During the flent rrul test, another machine in my home had started a Steam
> game update, this opened somewhere between 8-12 connections and saturated my
> downstream.
>
> The interesting part was the resulting rrul graph, showing perfect latency
> control during the test, but 100-150ms of bufferbloat at the very start and
> end of the rrul graph (when rrul is idle, just pinging).
>
> Instead of a Steam download I started an iperf3 client on a remote machine
> that opened 16 connections to a LAN machine. Same behavior as the Steam
> download.
>
> At first I thought this was a bug with cake, but no matter how I tuned cake
> (limiting my 400/40 connection to 50/20 for example), the behavior was
> similar.
> I tried fq_codel+htb, and got similar results to cake, high latency before
> the rrul test kicked off, great latency while rrul was doing its up and
> downloads.
>
> So I swapped out my self-compile LEDE router with an Edgerouter ER-X with
> both stock and LEDE firmware, both with fq_codel and cake (on both stock and
> LEDE firmware). Same results.
> Even without any SQM active, the rrul test still improved the latency of my
> connection when it's also downloading from 8+ connections at the same time.
>
> I managed to take the flent rrul test out of the equation by starting a
> hping3 "flood" to the hop next of my cable modem.
>
>> hping3 -2 -d 0 -s 10080 -k -p 80 -i u100
>> first-hop-or-ISP-gateway-goes-here
>
>
> This also fixed the latency while many downloads were running by sending
> about 300KB/s of empty UDP packets to some unresponsive port on my ISPs
> local gateway.
>
> I'm puzzled by this result, somehow sending 300KB/s of empty packets
> upstream drastically improves the latency of my connection when it's
> receiving many downloads.
>
> Equipment used:
> Cisco EPC3212 cable modem (8x4 EuroDOCSIS 3.0)
> Linksys WRT1900ACS router with LEDE
> Ubiquiti Edgerouter ER-X with both EdgeOS (stock) and LEDE
>
>
>
>
> _______________________________________________
> Bloat mailing list
> Bloat at lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/bloat
>



-- 

Dave Täht
CEO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-669-226-2619