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Problem:

The statistics used by minstrel_ht - Linux's typical WiFi bitrate adaptation algorithm - are published in the file /sys/kernel/debug/ieee80211/phy*/*/stations/*/rc_stats.

This file has a table-like structure. According to the sources I could find ([1, 2], didn't check the source code), I've understood that the letters in the 'best rate' column refer to special bitrates which then make part of Minstrel's 'retry chain':

  • T : highest throughput
  • t : second highest throughput
  • P : highest probability of success (i.e., delivery probability)

However, after inspecting the file myself I found a different set of letters: A, B, C, D, BP, CP and DP.

Question:

What is the meaning of the letters A, B, C, D, BP, CP and DP in the 'best rate' column of the /sys/kernel/debug/ieee80211/phy*/*/stations/*/rc_stats file?

I've made an experiment and collected the contents of the rc_stats_csv over a period of aprox. 2.5 minutes (results here), and verified that A is probably the equivalent to 'highest throughput', and B, C and D to 2nd, 3rd and 4th highest, respectively. The *P probably refer to the rates with better delivery probabilities.

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    "didn't check the source code" So go check the source code. – DavidPostill Dec 2 '18 at 17:27
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    @DavidPostill I thought it would be more difficult to find the answer in the code since I'm not familiar with browsing Linux kernel's code. Nevertheless, I've followed your advice and found the answer. I've answered my own question, since this may be useful to others. – fortune_pickle Dec 2 '18 at 17:54
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According to the rc80211_minstrel_ht_debugfs.c source file, minstrel_ht_stats_dump() method (available here), the letters in the 'best rate' column in the rc_stats file mean the following:

  • A : Highest throughput
  • B : 2nd highest throughput
  • C : 3rd highest throughput
  • D : 4th highest throughput
  • P : Maximum delivery probability

Cases with two letters, e.g. 'PA', mean when a bitrate is both the i-th highest in throughput and the one with the maximum delivery probability.

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