[Make-wifi-fast] On the ath9k performance regression with FQ and crypto

Toke Høiland-Jørgensen toke at toke.dk
Wed Aug 17 08:04:01 EDT 2016

Felix Fietkau <nbd at nbd.name> writes:

> I have not done any further tests, but based on your analysis, I think I
> finally understand what's causing this issue:
> The CCMP PN (crypto IV) is assigned in the tx path before a packet is
> put into the txq. It is also used to protect against replay attacks, so
> it is sensitive to reordering. The receiver is simply dropping any
> packet where the PN value is lower than the highest PN received so far.
> To fix this, we will have to move the IV/PN assignment to
> ieee80211_tx_dequeue.

Indeed this seems to be the cause of the problem. Thanks!

Will send a patch once we've run it through another couple rounds of
testing. Looks promising so far :)


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