[Codel] cake3 vs sqm+fq_codel at 115/12 mbit (basically comcast´s blast service)

Dave Taht dave.taht at gmail.com
Thu Apr 2 14:05:59 EDT 2015

this is with a special build of openwrt (not CeroWrt) on the tplink
archer c7v2. It rips out the unaligned access hacks, and is compiled
for the mips74k processor in that box.

Even with hostapd
running like crazy for no good reason, we do fq/aqm/ecn perfectly with cake3
at the 115/12 mbit rate now common from comcast, with about 5% cpu
left over, where the sqm+fq_codel version runs out of cpu and falls
apart you will see in the attached graphs....

For the longest time we were aiming for a piece of affordable hardware
that could do 300
Mbit download shaping, with no luck. On this low end (this box is  89
dollars on newegg),
maybe this is enough to get restarted with, while we wait for other
stuff to stablize.

The 115Mbit service from comcast exhibits about 230ms worth of latency
under load on downloads without this shaping in place, 5-25ms with it.
:) The uplink, well, I have data for it somewhere, but it isnt
pretty... and totally fixed by cake3 here also.

(I still have to benchmark ipv6, I want to share some joy, however
briefly, first.)

That test build is at:


DO NOT install this on any hardware that is not mips74k (e.g. dont try
the wndr3800). Do feel free to try anything in the above list that is

I would like to try an octeon build with cake3, to see if 115mbit can
be achieved there, too, but I think more performance analysis and
optimization is needed first.

Anyway, cake3 outputs a ton more statistics

root at OpenWrt:/# tc -s qdisc show dev eth1
qdisc cake3 8005: root refcnt 2 bandwidth 12Mbit diffserv4 flows
 Sent 437523173 bytes 1386559 pkt (dropped 4317, overlimits 1852389 requeues 0)
 backlog 0b 0p requeues 0
           Class 0     Class 1     Class 2     Class 3
  rate        12Mbit   11250Kbit       9Mbit       3Mbit
  target       5.0ms       5.0ms       5.0ms       6.1ms
interval     105.0ms     105.0ms     105.0ms     106.1ms
Pk delay       5.5ms       301us       295us       196us
Av delay       1.2ms        16us        32us        10us
Sp delay         2us         1us         2us         2us
  pkts        215134     1048937       10377      116428
way inds           4           0           0           0
way miss        4466         143           6          13
way cols           0           0           0           0
  bytes    160066252   257893148     1903096    24102496
  drops         4310           3           0           4
  marks         8037       52634           0       11451
-------------- next part --------------
A non-text attachment was scrubbed...
Name: fq_codel_sqm_archer.png
Type: image/png
Size: 96956 bytes
Desc: not available
URL: <https://lists.bufferbloat.net/pipermail/codel/attachments/20150402/8f13822e/attachment-0004.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: sqm_cake3_archer.png
Type: image/png
Size: 85009 bytes
Desc: not available
URL: <https://lists.bufferbloat.net/pipermail/codel/attachments/20150402/8f13822e/attachment-0005.png>

More information about the Codel mailing list