[Bloat] Curious bufferbloat on DOCSIS connection with many downloads

[Arie]

Not powersave of any component in my control. Powersave of the CMTS? I'd
expect high latency for idle pings in that case too.



On 16 January 2018 at 20:52, Dave Taht <dave.taht at gmail.com> wrote:

> 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
>
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