[WLANnews] Optimierung der Bandbreitenverteilung/Latenz mit fq_codel

[Ruben Kelevra]

Das hier klingt anders:

"However, today's Linux implementation of CoDel is imperfect: there
are typically (at least) one or more packets of buffering under the
Linux qdisc, in the device driver (or one packet in htb) even if BQL
is available. This means that the "head drop" of CoDel's design is not
actually a true head drop, but several packets back in in the actual
queue (since there is no packet loss at the device driver interface),
and that CoDel's square root computation is not exactly correct. These
effects are vanishingly small at 1Gbps or higher, but when used at low
speeds, even one packet of buffering is very significant; today's
fq_codel and codel qdiscs do not try to compensate for what can be
significant sojourn time of these packets at low bandwidth. So you
might have to "tune" the qdiscs in ways (e.g. the target) that in
principle the CoDel algorithm should not require when used at low
bandwidths. We hope to get this all straightened out someday soon, but
knowing exactly how much buffering is under a qdisc is currently
difficult and it isn't clear when this will happen.

When running it at 1GigE and lower, today it helps to change a few
parameters given limitations in today's Linux implementation and
underlying device drivers."

Quelle:

http://www.bufferbloat.net/projects/codel/wiki/Best_Practices_for_Benchmarking_CoDel_and_FQ_CoDel


LG Ruben

Am 25. August 2013 17:02 schrieb Felix Fietkau <nbd at openwrt.org>:
> On 2013-08-25 12:52 PM, Ruben Kelevra wrote:
>> Hat fq_codel nicht einen eigenen Puffer? Standardmäßig mit 10xxx Paketen?
>>
>> Ich war davon aus gegangen das der fq_codel-Puffer reicht um die Karte
>> mit Daten zu füllen.
> Die Puffertiefe von fq_codel richtet sich soweit ich weiß nach der
> netdev txqueuelen.
>
> - Felix
>