Okay - the 18.04.3 release I tested in September, which was fine, has
5.0.0-23.

-29 is broken, as mentioned above. That's a pretty narrow window to work with.
I'd prefer it if someone from Canonical took it from here.
(Heck, there are probably few enough commits to that driver in that timeframe 
that I could find the bad one more easily just by browsing the source than 
getting that machine to build it).

Since it's the HWE stack that's broken, I could still install 18.04 from the 
image I have and switch back to the original Bionic kernel series, though it's 
anybody's guess if the same regression was merged into 4.15 again as well.
Having to do a fresh install sucks pretty hard, but I'd at least be able to pin 
the last unbroken kernel, whereas on 19.10 there aren't any working ones in the 
repos at all (AFAIK) so I'm basically screwed until a fix makes its way through 
the system or I brute-force an older one onto it. I'm still trying to decide if 
I really want to go down that road or not.

I found https://people.canonical.com/~kernel/info/kernel-version-map.html , but 
it's basically useless. All the 4.15 kernels from the working -32 through the 7 
months of buggy ones and out the other side to -55 when it was fixed are all 
just "4.15.18 mainline".
Maybe I'm missing something here, but without the tree that you guys are 
*actually building from* I don't see how me bisecting mainline is going to 
achieve anything. If that page is accurate it has nothing to do with mainline 
at all and the bug only exists in the Ubuntu tree in the first place, neh?

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https://bugs.launchpad.net/bugs/1847892

Title:
  large performance regression (~30-40%) in wifi with 19.10 / 5.3 kernel

Status in linux package in Ubuntu:
  Confirmed

Bug description:
  Probably relevant:
  https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1795116

  Card is an RTL8723BE.

  On 16.04 with the HWE stack, after 1795116 was fixed performance was a
  stable 75-80Mb/s.

  Linux 4.15.0-55-generic #60~16.04.2-Ubuntu SMP Thu Jul 4 09:03:09 UTC 2019 
x86_64
  Fri 26-Jul-19 12:28
  sent 459,277,171 bytes  received 35 bytes  9,278,327.39 bytes/sec

  Linux 4.15.0-55-generic #60~16.04.2-Ubuntu SMP Thu Jul 4 09:03:09 UTC 2019 
x86_64
  Sat 27-Jul-19 01:23
  sent 459,277,171 bytes  received 35 bytes  10,320,836.09 bytes/sec

  On 18.04, performance was still a stable 75-80Mb/s.

  After updating to 19.10, performance is typically ~50Mb/s, or about a
  37% regression.

  $ iwconfig wlan0
  wlan0     IEEE 802.11  ESSID:"**"  
            Mode:Managed  Frequency:2.442 GHz  Access Point: 4C:60:DE:FB:A8:AB  
 
            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=59/70  Signal level=-51 dBm  
            Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
            Tx excessive retries:0  Invalid misc:315   Missed beacon:0

  $ ./wifibench.sh 
  Linux 5.3.0-13-generic #14-Ubuntu SMP Tue Sep 24 02:46:08 UTC 2019 x86_64
  Sat 12-Oct-19 20:30
  sent 459,277,171 bytes  received 35 bytes  5,566,996.44 bytes/sec

  $ iwconfig wlan0 
  wlan0     IEEE 802.11  ESSID:"**"  
            Mode:Managed  Frequency:2.442 GHz  Access Point: 4C:60:DE:FB:A8:AB  
 
            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=68/70  Signal level=-42 dBm  
            Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
            Tx excessive retries:0  Invalid misc:315   Missed beacon:0

  So no corrupted packets or etc during that transfer.

  $ ifconfig wlan0
  wlan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
          inet 192.168.1.33  netmask 255.255.255.0  broadcast 192.168.1.255
          ether dc:85:de:e4:17:a3  txqueuelen 1000  (Ethernet)
          RX packets 56608204  bytes 79066485957 (79.0 GB)
          RX errors 0  dropped 0  overruns 0  frame 0
          TX packets 21634510  bytes 8726094217 (8.7 GB)
          TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

  No issues of any kind in the week that it's been up. Just terrible
  performance.

  I'm painfully aware of all the module's parameters etc, and have tried
  them all, with no change in the results outside of typical wifi
  variance.

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