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16.04 install using the HWE stack. after several weeks of uptime on -32,
an update to -34 showed a major drop in wifi throughput, dependent
solely on the kernel chosen:
$ uname -a && ./wifibench.sh
Linux brix 4.15.0-32-generic #35~16.04.1-Ubuntu SMP Fri Aug 10 21:54:34 UTC
2018 x86_64 x86_64 x86_64 GNU/Linux
Tue 25-Sep-18 06:07
PlatformSDK-SVR2003R2.iso
429,840,384 100% 8.41MB/s 0:00:48 (xfr#1, to-chk=0/1)
sent 429,945,420 bytes received 35 bytes 8,685,766.77 bytes/sec
$ uname -a && ./wifibench.sh
Linux brix 4.15.0-34-generic #37~16.04.1-Ubuntu SMP Tue Aug 28 10:44:06 UTC
2018 x86_64 x86_64 x86_64 GNU/Linux
Tue 25-Sep-18 06:14
PlatformSDK-SVR2003R2.iso
429,840,384 100% 4.83MB/s 0:01:24 (xfr#1, to-chk=0/1)
sent 429,945,420 bytes received 35 bytes 5,028,601.81 bytes/sec
(the script is a simple rsync from a NAS. nothing in the NAS, or the
router, or the physical positions of the devices or etc etc has changed,
let alone in those 7 minutes).
there is no interference, no other devices connected, etc.
prior to the transfer, the link quality is 62-64 and the signal similarly
weaker because of power saving, but once packets are in flight it looks perfect:
$ iwconfig
wlan0 IEEE 802.11 ESSID:"****"
Mode:Managed Frequency:2.452 GHz Access Point: ****
Bit Rate=150 Mb/s Tx-Power=20 dBm
Retry short limit:7 RTS thr=2347 B Fragment thr:off
Power Management:on
Link Quality=70/70 Signal level=10 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:15 Missed beacon:0
the client is a J1900-based (baytrail) machine with a RTL8723BE wifi module.
average performance while on -32 was consistently 70-80 Mb/s, over a period of
several weeks. with -33 and later, it's generally 50-65.
(that machine has no access to launchpad. i'll try apport-cli over the weekend).
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: bot-comment kernel-bug wifi
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large performance regression (~20-40%) in wifi with 4.15.0-33 and later
https://bugs.launchpad.net/bugs/1795116
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