[Bloat] weird problem WRT1200 + CAKE on OpenWrt 18.06.2

[Mikael Abrahamsson <swmike@swm.pp.se>]

Hi,

I've been running openwrt 18.06.2 for a long time on my WRT1200AC, with 
CAKE, and everything has been great. I always got A+ in dslreports for 
bufferbloat. I have a 250/100 ETTH connection (IP over ethernet native, no 
PPPoE, no PON).

I noticed some intermittent network stuttering issues I wanted to diagnose 
last week, so I started looking into this. When doing the test I get 
+100ms spikes in the downstream direction when I run CAKE. If I instead 
switch to FQ_CODEL I do not see these spikes. As a matter of fact, if I 
set my downstream to 300 when running cake and let my ISP handle the 
buffering then I get an average of 5-10ms worth of buffering with no 
spikes. My ISP isn't bloated in that direction.

# tc qdisc show dev eth1.2
qdisc cake 801f: root refcnt 2 bandwidth 100Mbit diffserv3 triple-isolate nonat nowash no-ack-filter split-gso rtt 100.0ms noatm overhead 22
qdisc ingress ffff: parent ffff:fff1 ----------------

tc qdisc show dev ifb4eth1.2
qdisc cake 8020: root refcnt 2 bandwidth 240Mbit diffserv3 triple-isolate nonat nowash no-ack-filter split-gso rtt 100.0ms noatm overhead 22

http://www.dslreports.com/speedtest/52542158 is the result I get with 
above settings.

http://www.dslreports.com/speedtest/52542263 is the result with FQ_CODEL:

# tc qdisc show dev eth1.2
qdisc htb 1: root refcnt 2 r2q 10 default 18 direct_packets_stat 0 direct_qlen 1000
qdisc fq_codel 120: parent 1:12 limit 1001p flows 1024 quantum 300 target 5.0ms interval 100.0ms memory_limit 4Mb ecn
qdisc fq_codel 130: parent 1:13 limit 1001p flows 1024 quantum 300 target 5.0ms interval 100.0ms memory_limit 4Mb ecn
qdisc fq_codel 110: parent 1:11 limit 1001p flows 1024 quantum 300 target 5.0ms interval 100.0ms memory_limit 4Mb ecn
qdisc ingress ffff: parent ffff:fff1 ----------------

# tc qdisc show dev ifb4eth1.2
qdisc htb 1: root refcnt 2 r2q 10 default 18 direct_packets_stat 0 direct_qlen 32
qdisc fq_codel 120: parent 1:12 limit 1001p flows 1024 quantum 1500 target 5.0ms interval 100.0ms memory_limit 4Mb ecn
qdisc fq_codel 130: parent 1:13 limit 1001p flows 1024 quantum 300 target 5.0ms interval 100.0ms memory_limit 4Mb ecn
qdisc fq_codel 110: parent 1:11 limit 1001p flows 1024 quantum 500 target 5.0ms interval 100.0ms memory_limit 4Mb ecn

How do I diagnose this further?

-- 
Mikael Abrahamsson    email: swmike@swm.pp.se