[Bloat] Excessive throttling with fq

[Hans-Kristian Bakke <hkbakke@gmail.com>]

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Another day, another fq issue (or user error).

I try to do the seeminlig simple task of downloading a single large file
over local gigabit  LAN from a physical server running kernel 4.8 and
sch_fq on intel server NICs.

For some reason it wouldn't go past around 25 MB/s. After having replaced
SSL with no SSL, replaced apache with nginx and verified that there is
plenty of bandwith available between my client and the server I tried to
change qdisc from fq to pfifo_fast. It instantly shot up to around the
expected 85-90 MB/s. The same happened with fq_codel in place of fq.

I then checked the statistics for fq and the throttled counter is
increasing massively every second (eth0 and eth1 is LACPed using Linux
bonding so both is seen here):

qdisc fq 8007: root refcnt 2 limit 10000p flow_limit 100p buckets 1024
orphan_mask 1023 quantum 3028 initial_quantum 15140 refill_delay 40.0ms
 Sent 787131797 bytes 520082 pkt (dropped 15, overlimits 0 requeues 0)
 backlog 98410b 65p requeues 0
  15 flows (14 inactive, 1 throttled)
  0 gc, 2 highprio, 259920 throttled, 15 flows_plimit
qdisc fq 8008: root refcnt 2 limit 10000p flow_limit 100p buckets 1024
orphan_mask 1023 quantum 3028 initial_quantum 15140 refill_delay 40.0ms
 Sent 2533167 bytes 6731 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
  24 flows (24 inactive, 0 throttled)
  0 gc, 2 highprio, 397 throttled

Do you have any suggestions?

Regards,
Hans-Kristian

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