Re: [Bloat] AQM and PPP on Linux

[Dave Taht <dave.taht@gmail.com>]

On Tue, Jul 28, 2015 at 3:09 PM, Juliusz Chroboczek
<jch@pps.univ-paris-diderot.fr> wrote:
> I'm currently away from home, and using a 3G modem for Internet access.
> I've found out that both NetworkManager and wvdial/pppd setup the
> interface to use pfifo_fast (with a qlen of a mere 3 packets!).  Setting
> fq_codel manually appears to work fine, but needs to be redone every time
> the modem has a hiccup.
>
> Is that the expected behaviour?  Shouldn't we be pushing patches somewhere
> to change the default?

1) The ppp driver was debloated by david woodhouse way back when.

However, the netusb-related drivers, and the 3g devices themselves,
contain oft-huge buffers that reduce the effectiveness of any aqm or
fq system, sometimes to immeasurability.

I would be very interested in flent benchmarks of your 3g device with
the 3 packet txqueue and with fq_codel, for the tcp_upload, rrul, and
rrul_be tests.

2) Most advanced qdiscs ignore txqueuelen entirely.

3) Usually you can add a script in /etc/network/ifpreup.d or ifup.d to
do extra stuff you want.

4) setting the default qdisc to be fq_codel in the sysctl works on
most dynamically created devices, but does not work on devices that
come up at boot time before the sysctls have a chance to run and the
modprobes to complete. This is why fedora 22, for example, compiled in
fq_codel statically, rather than dynamically.


> -- Juliusz
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-- 
Dave Täht
worldwide bufferbloat report:
http://www.dslreports.com/speedtest/results/bufferbloat
And:
What will it take to vastly improve wifi for everyone?
https://plus.google.com/u/0/explore/makewififast