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

[Y]

Hi , Kathleen.

Fomula of target is 1643 bytes / 810kbps = 0.015846836.

It added ATM linklayer padding.




On 2017年11月03日 01:33, Kathleen Nichols wrote:
> On 11/2/17 1:25 AM, Sebastian Moeller wrote:
>> 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)...
> An MTU packet would cause 14.6ms of delay. To cause a codel drop, you'd
> need to have a queue of more than one packet hang around for 400ms. I
> would suspect if you looked at the dynamics of the delay you'll see it
> going up and down and probably averaging to something less than two
> packet times. Delay vs time is probably going to be oscillatory.
>
> Is the unloaded RTT on the order of 2-300 ms?
(When I do speedtest upload with ping to 8.8.8.8)
Ping RTT is around 30ms-80ms.
Avarage is around 40ms-50ms.
There is not 100ms over delay.
 >

Delay vs time is probably going to be oscillatory.

yes :)

>> 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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