[Codel] R: Making tests on Tp-link router powered by Openwrt svn

Jim Gettys jg at freedesktop.org
Fri Dec 21 13:30:06 EST 2012

On Fri, Dec 21, 2012 at 12:51 PM, Alessandro Bolletta <
alessandro at mediaspot.net> wrote:

> Hi everybody,
> Thanks so much for your useful help! I solved my problem by reproducing
> bottleneck through HTB queues.
> I tried some bandwidth rates and i saw that target must be increased if
> the available bandwidth is <4mbps. 13ms is a good compromise for that
> situation.
> Also, i removed the switch from my testbed.
> Codel works amazingly well, congratulations for the job that has been done!
> I'll try to make more tests to ensure that it will be suitable for our
> needs; we are building a new wireless mesh network in Italy based on a
> totally new architecture and Codel could be a great improvement for queue
> management on the nodes.
> Thanks again for your courtesy!
> Alessandro Bolletta


So in this case, there is another packet of buffering *under* the codel
queue in the HTB line discipline (which buffers one packet), plus whatever
additional buffering of there may be in the device driver (where the
mileage varies).

So codel isn't actually dropping the head of the queue, but the second (or
further) packet back, in effect.  So the control law computation won't be
quite right.
                          - Jim
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