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

["Toke Høiland-Jørgensen" <toke@toke.dk>]

Felix Fietkau <nbd@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.

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

-Toke