[FS#1136] HFSC kernel warnings with QoS / SQM

[LEDE Bugs]

The following task has a new comment added:

FS#1136 - HFSC kernel warnings with QoS / SQM
User who did this - Tony Ambardar (guidosarducci)

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I actually couldn't wait to try, and managed to do an A/B comparison for stable LEDE 17.01.04 with/without the patch. I tested hfsc with fq-codel, codel, and cake, under 1-hour of network load using [[https://github.com/richb-hanover/CeroWrtScripts/blob/master/netperfrunner.sh|netperfrunner.sh]] from [[https://www.bufferbloat.net/projects/bloat/wiki/Tests_for_Bufferbloat/|bufferbloat.net]].

====Results====

System & Kernel (ar71xx) | hfsc+fq_codel  |   hfsc+codel   |   hfsc+cake
------------------------ | -------------- | -------------- | --------------
LEDE 17.01.4 (stock)     | WARNING < 1min |   No warning   |   No warning
LEDE 17.01.4 (hfsc_fix)  |   No Warning   |   No Warning   |   No Warning


====Notes====

  * The patch does seem to address past problems with **hfsc** + **fq_codel**.
  * I've never encountered problems with **codel**, although the patch updates it too.
  * I've never encountered problems with **hfsc** + **cake**. I tested since cake borrows from **fq_codel**, but it appears to handle dequeue and zero qlen differently. (How to ping Jonathan Morton from here?)

I won't be able to test this for **master** branch, but 4.9 and 4.14 are closer to the patch's original target so I expect similar results. I will continue to use my patched system as "daily driver" and report if there are problems.

If we can get some more test runtime and architecture diversity, hopefully this can be back-ported to LEDE stable.
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More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=1136#comment4452