Re: [Bloat] Any aqm evaluation at speeds >=10Gbit/s?

[Alan Jenkins <alan.christopher.jenkins@gmail.com>]

On 19/05/15 14:04, Bless, Roland (TM) wrote:
> Hi,
>
> has anyone recently tested AQMs like Codel or PIE
> at speeds of >=10Gbit/s? If so, where are the results available?
> Pointers greatly appreciated...
>
> Regards,
>   Roland

I know only background information on that.

1) fq_codel was written by Eric Dumazet of Google and tested at 10G. 
Allegedly at 10G CoDel works fine, and fq_codel costs "2% of a single 
modern CPU core".  Sounds trustworthy but that doesn't give you any 
details :).  Cite: Jim Gettys.

Codel: 
https://gettys.wordpress.com/2012/05/22/a-milestone-reached-codel-is-in-linux/
fq_codel: https://www.ietf.org/proceedings/87/slides/slides-87-aqm-6.pdf


[Whether router queue management can achieve anything for a 10g link 
which also has high multiplexing and 50%+ exponential 'slow start' with 
IW10...  I think we didn't have an answer ready when that came up.]


2) Eric also wrote sch_fq and tested it at 10G.  sch_fq is only designed 
for end hosts and is not designed or implemented to reduce latency AIUI.


[I may finally understand this article

https://lwn.net/Articles/564978/

For our bufferbloat at the ISP network edge, the more important part of 
the article is TSO sizing.  Which does not depend on qdisc.

sch_fq just does TCP pacing (and flow queuing).

sch_fq pacing doesn't affect slow start _or_ saturating ("ack clocked") 
flows, which are the causes of edge bufferbloat.  It could do, but 
Eric's next priority is to improve TCP congestion control.

https://lists.bufferbloat.net/pipermail/bloat/2015-April/002797.html
https://lists.bufferbloat.net/pipermail/bloat/2015-April/002801.html]

What does sch_fq actually pace?  Well, "you no longer have to
slow start after idle", so it should help things like re-used HTTP 
connections.  But I think the implication is also for consistent flows 
that don't saturate: media streaming.

https://lists.bufferbloat.net/pipermail/bloat/2015-April/002764.html]


Alan