[Bloat] Tuning fq_codel: are there more best practices for slow connections? (<1mbit)

[Sebastian Moeller]

Hi Y.


> On Nov 2, 2017, at 07:42, Y <intruder_tkyf at yahoo.fr> wrote:
> 
> hi.
> 
> My connection is 810kbps( <= 1Mbps).
> 
> This is my setting For Fq_codel,
> quantum=300
> 
> target=20ms
> interval=400ms
> 
> MTU=1478 (for PPPoA)
> I cannot compare well. But A Latency is around 14ms-40ms.

	Under full saturation in theory you would expect the average latency to equal the sum of upstream target and downstream target (which in your case would be 20 + ???) in reality I often see something like 1.5 to 2 times the expected value (but I have never inquired any deeper, so that might be a measuring artifact)...

Best Regards


> 
> Yutaka.
> 
> On 2017年11月02日 15:01, cloneman wrote:
>> I'm trying to gather advice for people stuck on older connections. It appears that having dedictated /micromanged tc classes greatly outperforms the "no knobs" fq_codel approach for connections with  slow upload speed.
>> 
>> When running a single file upload @350kbps , I've observed the competing ICMP traffic quickly begin to drop (fq_codel) or be delayed considerably ( under sfq). From reading the tuning best practices page is not optimized for this scenario. (<2.5mbps)
>> (https://www.bufferbloat.net/projects/codel/wiki/Best_practices_for_benchmarking_Codel_and_FQ_Codel/) fq_codel 
>> 
>> Of particular concern is that a no-knobs SFQ works better for me than an untuned codel ( more delay but much less loss for small flows). People just flipping the fq_codel button on their router at these low speeds could be doing themselves a disservice.
>> 
>> I've toyed with increasing the target and this does solve the excessive drops. I haven't played with limit and quantum all that much. 
>> 
>> My go-to solution for this would be different classes, a.k.a. traditional QoS. But ,  wouldn't it be possible to tune fq_codel punish the large flows 'properly' for this very low bandwidth scenario? Surely <1kb ICMP packets can squeeze through properly without being dropped if there is 350kbps available, if the competing flow is managed correctly.
>> 
>> I could create a class filter by packet length, thereby moving ICMP/VoIP to its own tc class, but  this goes against "no knobs" it seems like I'm re-inventing the wheel of fair queuing - shouldn't the smallest flows never be delayed/dropped automatically?
>> 
>> Lowering Quantum below 1500 is confusing, serving a fractional packet in a time interval?
>> 
>> Is there real value in tuning fq_codel for these connections or should people migrate to something else like nfq_codel?
>> 
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