Had the affected machine in here (i.e. "where the router is") for other
reasons, so I was able to check those conditions too. As expected, it's
a power / antenna / etc issue:
Linux 5.3.0-19-generic #20-Ubuntu SMP Fri Oct 18 09:04:39 UTC 2019 x86_64
Fri 08-Nov-19 03:29
sent 459,277,171 bytes received 35 bytes 7,467,922.05 bytes/sec
iwlist scan, WHILE the rsync was running (so it shouldn't be power-saving at
all) with the router 6' away with clear LOS showed:
Frequency:2.422 GHz (Channel 3)
Quality=62/70 Signal level=-48 dBm
Looking at 1795116, I used to get 70/70 at -32 dBm upstairs and through half a
dozen walls, so obviously this is a significant drop in link quality given the
hugely better conditions.
Compared to 4.15.0-36 - which, bear in mind was one of the BROKEN kernels, the
performance is 7,467,922 / 11,167,414, or 66.9% of what it should be in that
scenario.
The good news is, that difference suggests it's at least not a simple
merge regression of 1795116. The bad news is, of course, that it'll need
a new round of investigation track down.
As I've said, I'm willing to set things up to help out, but I'm still
waiting for you to provide me with the ACTUAL Ubuntu kernel tree to
bisect against. In the meantime, I'll probaby try a couple of the
mainline builds since I can just dpkg those, but with no way to map the
working Ubuntu ones to the mainline tree I'll never have a baseline to
compare against in case something stupid has happened like one of the
antenna connectors has become disconnected or etc.
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https://bugs.launchpad.net/bugs/1847892
Title:
large performance regression (~30-40%) in wifi with 19.10 / 5.3 kernel
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