> on channel 8(+4), 4.19 typically performed on par with -32 and older.
apparently only because of some fluke. the router switched to 4(+8) some
time in the past couple of days, and the newer kernels are certainly
sucking hard on that too:
---
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
Current Frequency:2.427 GHz (Channel 4)
Link Quality=70/70 Signal level=-36 dBm
Sun 07-Oct-18 03:30
429,840,384 100% 9.00MB/s 0:00:45 (xfr#1, to-chk=0/1)
sent 429,945,420 bytes received 35 bytes 9,449,350.66 bytes/sec
---
Linux brix 4.15.0-36-generic #39~16.04.1-Ubuntu SMP Tue Sep 25 08:59:23 UTC
2018 x86_64 x86_64 x86_64 GNU/Linux
Current Frequency:2.427 GHz (Channel 4)
Link Quality=64/70 Signal level=-46 dBm
Sun 07-Oct-18 05:05
429,840,384 100% 6.46MB/s 0:01:03 (xfr#1, to-chk=0/1)
sent 429,945,420 bytes received 35 bytes 6,665,821.01 bytes/sec
---
this is a major regression. is there any activity on it upstream?
i can't imagine it's ALL wifi, or people would be screaming for blood,
but it would be good to at least get it in front of larry finger (the
rtl driver author) as a starting point.
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https://bugs.launchpad.net/bugs/1795116
Title:
large performance regression (~20-40%) in wifi with 4.15.0-33 and
later
Status in linux package in Ubuntu:
Confirmed
Bug description:
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).
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