[Make-wifi-fast] [PATCH v7] mac80211: Move reorder-sensitive TX handlers to after TXQ dequeue.

Felix Fietkau nbd at nbd.name
Mon Sep 5 14:45:04 EDT 2016

On 2016-09-05 19:59, Toke Høiland-Jørgensen wrote:
> Felix Fietkau <nbd at nbd.name> writes:
>> On 2016-09-05 13:30, Toke Høiland-Jørgensen wrote:
>>> The TXQ intermediate queues can cause packet reordering when more than
>>> one flow is active to a single station. Since some of the wifi-specific
>>> packet handling (notably sequence number and encryption handling) is
>>> sensitive to re-ordering, things break if they are applied before the
>>> TXQ.
>>> This splits up the TX handlers and fast_xmit logic into two parts: An
>>> early part and a late part. The former is applied before TXQ enqueue,
>>> and the latter after dequeue. The non-TXQ path just applies both parts
>>> at once.
>>> Because fragments shouldn't be split up or reordered, the fragmentation
>>> handler is run after dequeue. Any fragments are then kept in the TXQ and
>>> on subsequent dequeues they take precedence over dequeueing from the FQ
>>> structure.
>>> This approach avoids having to scatter special cases for when TXQ is
>>> enabled, at the cost of making the fast_xmit and TX handler code
>>> slightly more complex.
>> In my test, this one completely breaks ath9k with the txq patch.
>> One or two packets go through, then tx stalls completely.
> I assume you are testing on LEDE? It requires a change to work with the
> patch in the LEDE tree that puts hdrlen into ieee80211_tx_data. Did you
> fix that? Otherwise multicast (and possibly other things) will break
> badly.
You're right, I missed that.

> I have a version that should work with LEDE here:
> https://kau.toke.dk/git/lede/tree/package/kernel/mac80211/patches/346-mac80211-move-reorder-sensitive-tx-handlers-to-after-TXQ-dequeue.patch
That one works fine in my test.


- Felix

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