[FS#508] ath9k / poor performance + drops with r3426 (after airtime-fairness fixup)

[LEDE Bugs]

The following task has a new comment added:

FS#508 - ath9k / poor performance + drops with r3426 (after airtime-fairness fixup)
User who did this - Baptiste Jonglez (bjonglez)

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On a TL-WA850RE, I see no significant difference before and after the patch, and with/without airtime fairness.

Tested:

- lede-17.01-rc2 with airtime_flags set to 7
- lede-17.01-rc2 with airtime_flags set to 0
- r3439-d5221d5 with airtime_flags set to 7
- r3439-d5221d5 with airtime_flags set to 0

doesn't make much difference performance-wise...

Single station (Intel 7260 using iwlwifi), no encryption, uni- and bi-directional test using iperf through the router (one laptop on wireless and one laptop on wired).
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=508#comment1790