[Cerowrt-devel] uplink_buffer_adjustment

Jim Gettys jg at freedesktop.org
Tue Feb 25 10:59:58 EST 2014

On Tue, Feb 25, 2014 at 6:14 AM, Oliver Niesner <oliver.niesner at gmail.com>wrote:

> Hi list,
> I use cerowrt (3.10.24-8) direct behind my main dsl Router.
> SQM is set and performance is good.
> When i used Netalyzr from my smartphone i've got good results.
> > Network buffer measurements (?): Uplink 96 ms, Downlink is good
> But when i use my notebook i get this:
> > Network buffer measurements (?): Uplink 1200 ms, Downlink is good
> I tried even wired connection and set ring buffer rx/tx with ethtool to
> 64, but
> only minimal change in uplink buffer (1100ms).
> Has anyone an idea, what i can try to get better uplink performance?

Netalyzr uses a UDP based test for "filling the buffers"; it is not
responsive to drops/marks at all, the way a TCP test would be.

So if you run it, the flows it generates are unresponsive, and indicate the
true size of the buffers at the bottleneck link, even though any normal TCP
would long since have responded and nothing like that amount of buffering
would have taken place.  Furthermore, the flow queuing of fq_codel isolates
those flows from other flows, and therefore you do not get the bad latency
you would otherwise get on those flows.

In short, (particularly since fq_codel is deployed in quantity millions by
a few ISP's already; it is no longer a fluke to find it only in hacker's
hands), Nick Weaver needs to improve netalyzr to detect flow queuing
algorithms and make some sense out of the situation.  It would be great to
monitor the spread of these algorithms around the Internet over the coming

So it is arguably a "bug" in netalyzr.  It is certainly extremely


                                             - Jim

> Regards,
> Oliver
> _______________________________________________
> Cerowrt-devel mailing list
> Cerowrt-devel at lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/cerowrt-devel
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