[Bloat] Still seeing bloat with a DOCSIS 3.1 modem

[Dave Taht]

I just finished doing my first openwrt build in a couple years. (with
AQL) Trying to summon up the moxie to try it. Found my soldiering iron
and usb to serial interfaces....


On Wed, Mar 25, 2020 at 8:58 AM Aaron Wood <woody77 at gmail.com> wrote:
>
> One other thought I've had with this, is that the apu2 is multi-core, and the i210 is multi-queue.
>
> Cake/htb aren't, iirc, setup to run on multiple cores (as the rate limiters then don't talk to each other).  But with the correct tuple hashing in the i210, I _should_ be able to split things and do two cores at 500Mbps each (with lots of compute left over).

A good test might be sch_mq + cake bandwidth whatever for each hw
queue. irqbalancing also may or may not help.

> Obviously, that puts a limit on single-connection rates, but as the number of connections climb, they should more or less even out (I remember Dave Taht showing the oddities that happen with say 4 streams and 2 cores, where it's common to end up with 3 streams on the same core).  But assuming that the hashing function results in even sharing of streams, it should be fairly balanced (after plotting some binomial distributions with higher "n" values).  Still not perfect, especially since streams aren't likely to all be elephants.

One reason why we are seeing "tcp rack" pushed so hard is due to cable
modems having multiple channels, and thus ooo packets are probable
when you try to push a stream across those channels.

Me, I'm reasonably confident we've hit the age of "peak bandwidth" for
most things at up/dl rates above 40Mbit.

And in the real world at home, a couple hash collissions and unequal
distribution really don't matter for real traffic.

>
> On Wed, Mar 25, 2020 at 4:03 AM Toke Høiland-Jørgensen <toke at toke.dk> wrote:
>>
>> Sebastian Moeller <moeller0 at gmx.de> writes:
>>
>> > Hi Toke,
>> >
>> >
>> >> On Mar 25, 2020, at 09:58, Toke Høiland-Jørgensen <toke at toke.dk> wrote:
>> >>
>> >> Aaron Wood <woody77 at gmail.com> writes:
>> >>
>> >>> I recently upgraded service from 150up, 10dn Mbps to xfinity's gigabit
>> >>> (with 35Mbps up) tier, and picked up a DOCSIS 3.1 modem to go with it.
>> >>>
>> >>> Flent test results are here:
>> >>> https://burntchrome.blogspot.com/2020/03/bufferbloat-with-comcast-gigabit-with.html
>> >>>
>> >>> tl/dr;  1000ms of upstream bufferbloat
>> >>>
>> >>> But it's DOCSIS 3.1, so why isn't PIE working?  Theory:  It's in DOCSIS 3.0
>> >>> upstream mode based on the status LEDs.  Hopefully it will go away if I can
>> >>> convince it to run in DOCSIS 3.1 mode.
>> >>
>> >> I think that while PIE is "mandatory to implement" in DOCSIS 3.1, the
>> >> ISP still has to turn it on? So maybe yelling at them will work? (ha!)
>> >>
>> >>> At the moment, however, my WRT1900AC isn't up to the task of dealing with
>> >>> these sorts of downstream rates.
>> >>>
>> >>> So I'm looking at the apu2, which from this post:
>> >>> https://forum.openwrt.org/t/comparative-throughput-testing-including-nat-sqm-wireguard-and-openvpn/44724
>> >>>
>> >>> Will certainly get most of the way there.
>> >>
>> >> My Turris Omnia is doing fine on my 1Gbps connection (although that
>> >> hardly suffers from bloat, so I'm not doing any shaping; did try it
>> >> though, and it has no problem with running CAKE at 1Gbps).
>> >
>> >       Well, doing local network flent RRUL stress tests indicated that
>> >       my omnia (at that time with TOS4/Openwrt18) only allowed up to
>> >       500/500 Mbps shaping with bi directionally saturating traffic
>> >       with full MTU-sized packets. So I undirectional CAKE at 1Gbps
>> >       can work, but under full load, I did not manage that, what did I
>> >       wrong?
>>
>> Hmm, not sure I've actually done full bidirectional shaping. And trying
>> it now, it does seem to be struggling...
>>
>> -Toke
>
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-- 
Make Music, Not War

Dave Täht
CTO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-831-435-0729