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

From: "Bless, Roland (TM)" <[email-masked]>
Date: Tue, 19 May 2015 15:04:29 +0200

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

---

From: Alan Jenkins <[email-masked]>
Date: Tue, 19 May 2015 22:00:46 +0100

> Pointers greatly appreciated...

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