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SubjectRTL8723BE performance regression

I've been trying to track a performance regression on the RTL8723BE
WiFi adapter, which mainly affects the upload bandwidth (although we
can see a decreased download performance as well, the effect on upload
is more drastic). This was first reported by users after upgrading
from our 4.11-based kernel to our 4.13-based kernel, but also
confirmed to affect our development branch (4.15-based kernel) and
wireless-drivers-next at the
wireless-drivers-next-for-davem-2018-03-29 tag. This is happening on
an HP laptop that needs rtl8723be.ant_sel=1 (and all the following
tests have been made with that param).

My first bisect attempt pointed me to the following commit:

bcd37f4a0831 rtlwifi: btcoex: 23b 2ant: let bt transmit when hw
initialisation done

Which I later found to be already fixed by

a33fcba6ec01 rtlwifi: btcoexist: Fix breakage of ant_sel for rtl8723be.

That fix is already included in v4.15 though (and our dev branch as
well), so I did a second bisect, now cherry-picking a33fcba6ec01 at
every step, and it pointed me to the following commit:

7937f02d1953 rtlwifi: btcoex: hook external functions for newer chips

Reverting that commit on top of our development branch fixes the
problem, but on top of v4.15 I get mixed results: a few times getting
a good upload performance (~5-6Mbps) but most of the time just getting
~1-1.5Mpbs (which is still better than the 0.0 then test failure I've
gotten on most bad points of the bisect).

Bisecting the downstream patches we carry on top of v4.15 (we base our
kernel on Ubuntu's, so there are quite a few downstream changes) did
not bring any clarity, as at all bisect points (plus reverting
7937f02d1953) the performance was good, so probably there was some
other difference in the resulting kernels from my initial revert of
that patch on top of v4.15 and each step during the bisect. I've
experimented a bit with fwlps=0, but it did not bring any conclusive
results either. I'll try to look at other things that may have changed
(configuration perhaps?), but I don't have a clear plan yet.

Have you seen anything similar, or have any other ideas or suggestions
to track this problem? Even without crystal clear results, it looks
like 7937f02d1953 is having a negative impact on the RTL8723BE
performance, so perhaps it is worth reverting it and reworking it a
later point?

This are the results (testing with I got at some key points:

Version Commit Ping Down Up

v4.11 a351e9b 12 25.44 5.99
v4.11 a351e9b 131 17.02 5.89

v4.13 569dbb8 174 14.08 0.00
v4.13 569dbb8 261 8.41 0.00

v4.15+revert d8a5b80 19 23.86 1.41
v4.15+revert d8a5b80 189 18.69 1.39

Best regards,

João Paulo Rechi Vita

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