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| /freebsd-11-stable/sys/dev/ath/ | ||
| H A D | if_ath.c | diff 241559 Sun Oct 14 18:49:18 MDT 2012 adrian Push the actual TX processing into the ath taskqueue, rather than having it run out of multiple concurrent contexts. Right now the ath(4) TX processing is a bit hairy. Specifically: * It was running out of ath_start(), which could occur from multiple concurrent sending processes (as if_start() can be started from multiple sending threads nowdays.. sigh) * during RX if fast frames are enabled (so not really at the moment, not until I fix this particular feature again..) * during ath_reset() - so anything which calls that * during ath_tx_proc*() in the ath taskqueue - ie, TX is attempted again after TX completion, as there's now hopefully some ath_bufs available. * Then, the ic_raw_xmit() method can queue raw frames for transmission at any time, from any net80211 TX context. Ew. This has caused packet ordering issues in the past - specifically, there's absolutely no guarantee that preemption won't occuring _during_ ath_start() by the TX completion processing, which will call ath_start() again. It's a mess - 802.11 really, really wants things to be in sequence or things go all kinds of loopy. So: * create a new task struct for TX'ing; * make the if_start method simply queue the task on the ath taskqueue; * make ath_start() just be called by the new TX task; * make ath_tx_kick() just schedule the ath TX task, rather than directly calling ath_start(). Now yes, this means that I've taken a step backwards in terms of concurrency - TX -and- RX now occur in the same single-task taskqueue. But there's nothing stopping me from separating out the TX / TX completion code into a separate taskqueue which runs in parallel with the RX path, if that ends up being appropriate for some platforms. This fixes the CCMP/seqno concurrency issues that creep up when you transmit large amounts of uni-directional UDP traffic (>200MBit) on a FreeBSD STA -> AP, as now there's only one TX context no matter what's going on (TX completion->retry/software queue, userland->net80211->ath_start(), TX completion -> ath_start()); but it won't fix any concurrency issues between raw transmitted frames and non-raw transmitted frames (eg EAPOL frames on TID 16 and any other TID 16 multicast traffic that gets put on the CABQ.) That is going to require a bunch more re-architecture before it's feasible to fix. In any case, this is a big step towards making the majority of the TX path locking irrelevant, as now almost all TX activity occurs in the taskqueue. Phew. |
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