the machine is usually ~20 feet away from the router, through multiple
walls and a floor. i moved it last night so it was 6 feet away with LOS,
and the results from that are very interesting:
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:2.452 GHz (Channel 9)
Link Quality=70/70 Signal level=-30 dBm
Sat 20-Oct-18 17:23
429,840,384 100% 10.91MB/s 0:00:37 (xfr#1, to-chk=0/1)
sent 429,945,420 bytes received 35 bytes 11,167,414.42 bytes/sec
and under the same ideal conditions:
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:2.452 GHz (Channel 9)
Link Quality=70/70 Signal level=-32 dBm
Sat 20-Oct-18 17:29
429,840,384 100% 9.10MB/s 0:00:45 (xfr#1, to-chk=0/1)
sent 429,945,420 bytes received 35 bytes 9,449,350.66 bytes/sec
so the newer kernel is MUCH better in that situation, whereas the old kernel
essentially performs exactly the same.
the machine has a fairly weak cpu, and basically has one core pegged with
iowait during these transfers, so optimisations (either in general for meltdown
etc, or the stack, or in the driver specifically) could certainly account for
that sort of speedup.
however, that only further highlights just how bad this regression is,
because the driver is now nearly 20% faster in the abstract but still
massively slower at range despite all that improvement.
it also explains why nobody would notice the regression during
development.
i'm happy to test proposed fixes or provide more information, but i
don't think there's anything more i can do at my end until somebody else
steps in.
@joseph - do you have a tracking reference for upstream yet?
TIA
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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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