[Make-wifi-fast] tx queue stuck for many minutes

[Joshua Zhao <swzhao@gmail.com>]

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Hi,
I run into a weird symptom that occasionally the aqm tx queue can get stuck
for quite long time (maybe around 30min).  What happened is that we're
sending a low bandwidth UDP traffic from the host to multiple peers over a
WiFi radio simultaneously. We're running opensource mac80211 + ath10k
driver. Very occasionally when there are temporary issues causing trouble
on the host sending to one of the peers, the queue to all peers can get
stuck and stay stuck for quite long (even though the link trouble had been
gone or TX had been stopped). Only after quite a while, then the queue
cleans up.
The following dump shows an example that the backlog-packets count stays at
74 for around 30min after the TX had totally stopped. Here when video queue
is stuck, other TID's traffic can go through.
I wonder why it takes so long for the queue to clean up. Shouldn't packets
be dropped quickly if they cannot be sent?

Many thanks!

cat /sys/kernel/debug/ieee80211/phy0/netdev:wlan3/stations/xx:xx:xx/aqm

target 19999us interval 99999us ecn yes

tid ac backlog-bytes backlog-packets new-flows drops marks overlimit
collisions tx-bytes tx-packets

0 2 0 0 3 0 0 0 0 390 3

1 3 0 0 0 0 0 0 0 0 0

2 3 0 0 0 0 0 0 0 0 0

3 2 0 0 0 0 0 0 0 0 0

4 1 0 0 0 0 0 0 0 0 0

5 1 112344 74 1627 0 0 0 0 2373618 1632

6 0 0 0 0 0 0 0 0 0 0

7 0 0 0 1 0 0 0 0 32 1

8 2 0 0 0 0 0 0 0 0 0

9 3 0 0 0 0 0 0 0 0 0

10 3 0 0 0 0 0 0 0 0 0

11 2 0 0 0 0 0 0 0 0 0

12 1 0 0 0 0 0 0 0 0 0

13 1 0 0 0 0 0 0 0 0 0

14 0 0 0 0 0 0 0 0 0 0

15 0 0 0 0 0 0 0 0 0 0

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