When frames are sent over the air, the device always applies the data
rates in descending order. The driver assumed Minstrel also provided
rate in descending order.
However, in some cases, Minstrel can a choose a fallback rate greater
than the primary rate. In this case, the two rates was inverted, the
device try highest rate first and we get many retries.
Since the device always applies rates in descending order, the
workaround is to drop the rate when it higher than its predecessor in
the rate list. Thus [ 4, 5, 3 ] becomes [ 4, 3 ].
This patch has been tested in isolated room with a series of
attenuators. Here are the Minstrel statistics with 80dBm of attenuation:
Without the fix:
best ____________rate__________ ____statistics___ _____last____ ______sum-of________
mode guard # rate [name idx airtime max_tp] [avg(tp) avg(prob)] [retry|suc|att] [#success | #attempts]
HT20 LGI 1 S MCS0 0 1477 5.6 5.2 82.7 3 0 0 3 4
HT20 LGI 1 MCS1 1 738 10.6 0.0 0.0 0 0 0 0 1
HT20 LGI 1 D MCS2 2 492 14.9 13.5 81.5 5 0 0 5 9
HT20 LGI 1 C MCS3 3 369 18.8 17.6 84.3 5 0 0 76 96
HT20 LGI 1 A P MCS4 4 246 25.4 22.4 79.5 5 0 0 11268 14026
HT20 LGI 1 B S MCS5 5 185 30.7 19.7 57.7 5 8 9 3918 9793
HT20 LGI 1 MCS6 6 164 33.0 0.0 0.0 5 0 0 6 102
HT20 LGI 1 MCS7 7 148 35.1 0.0 0.0 0 0 0 0 44
With the fix:
best ____________rate__________ ____statistics___ _____last____ ______sum-of________
mode guard # rate [name idx airtime max_tp] [avg(tp) avg(prob)] [retry|suc|att] [#success | #attempts]
HT20 LGI 1 S MCS0 0 1477 5.6 1.8 28.6 1 0 0 1 5
HT20 LGI 1 DP MCS1 1 738 10.6 9.7 82.6 4 0 0 14 34
HT20 LGI 1 MCS2 2 492 14.9 9.2 55.4 5 0 0 52 77
HT20 LGI 1 B S MCS3 3 369 18.8 15.6 74.9 5 1 1 417 554
HT20 LGI 1 A MCS4 4 246 25.4 16.7 59.2 5 1 1 13812 17951
HT20 LGI 1 C S MCS5 5 185 30.7 14.0 41.0 5 1 5 57 640
HT20 LGI 1 MCS6 6 164 33.0 0.0 0.0 0 0 1 0 48
HT20 LGI 1 S MCS7 7 148 35.1 0.0 0.0 0 0 0 0 36
We can notice the device try now to send with lower rates (and high
success rates). At the end, we measured 20-25% better throughput with
this patch.
Fixes: 9bca45f3d6 ("staging: wfx: allow to send 802.11 frames")
Tested-by: Olivier Souloumiac <olivier.souloumiac@silabs.com>
Tested-by: Alexandr Suslenko <suslenko.o@ajax.systems>
Reported-by: Alexandr Suslenko <suslenko.o@ajax.systems>
Co-developed-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Signed-off-by: Felipe Negrelli Wolter <felipe.negrelliwolter@silabs.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231004123039.157112-1-jerome.pouiller@silabs.com
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