[Bloat] [Bug 1436945] Re: devel: consider fq_codel as the default qdisc for networking

[Sebastian Moeller]

Hi Jonathan,


> On Jun 5, 2018, at 17:10, Jonathan Foulkes <jf at jonathanfoulkes.com> wrote:
> 
> Jonathan, in the past the recommendation was for NOECN on egress if capacity <4Mbps. Is that still the case in light of this?
> 
> Thanks,
> 
> Jonathan Foulkes
> 
>> On Jun 4, 2018, at 5:36 PM, Jonathan Morton <chromatix99 at gmail.com> wrote:
>> 
>>> On 4 Jun, 2018, at 9:22 pm, Jonas Mårtensson <martensson.jonas at gmail.com> wrote:
>>> 
>>> Speaking about systemd defaults, they just enabled ecn for outgoing connections:
>> 
>> That is also good news.  With Apple *and* Ubuntu using it by default, we should finally get critical mass of ECN traffic and any remaining blackholes fixed, making it easy for everyone else to justify turning it on as well.

	The rationale for that decision still is valid, at low bandwidth every opportunity to send a packet matters and every packet being transferred will increase the queued packets delay by its serialization delay. The question IMHO is more is 4 Mbps a reasonable threshold to disable ECN or not.
Here are the serialization delays for a few selected bandwidths:

1000*(1538*8)/(500*1000)  = 24.61 ms
1000*(1538*8)/(1000*1000)  = 12.30 ms
1000*(1538*8)/(2000*1000)  = 6.15 ms
1000*(1538*8)/(4000*1000)  = 3.08 ms
1000*(1538*8)/(8000*1000) = 1.54 ms
1000*(1538*8)/(10000*1000) = 1.23 ms
1000*(1538*8)/(12000*1000) = 1.03 ms

Personally, I guess I sort of agree with the <= 4Mbps threshold, maybe 2Mbps, but at <=1Mbps the serialization delay gets painful.  

In sqm-scripts we currently unconditionally default to egress(ECN) off, which might be to pessimistic about the usual egress bandwidths.


Best Regards

>> 
>> - Jonathan Morton
>> 
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