> -----Original Message----- > From: ath10k <ath10k-bounces@xxxxxxxxxxxxxxxxxxx> On Behalf Of Erik > Stromdahl > Sent: Saturday, August 24, 2019 9:49 PM > To: Kalle Valo <kvalo@xxxxxxxxxxxxxxxx>; linux-wireless@xxxxxxxxxxxxxxx; > ath10k@xxxxxxxxxxxxxxxxxxx > Cc: Erik Stromdahl <erik.stromdahl@xxxxxxxxx> > Subject: [EXT] [PATCH] ath10k: remove TX lock from > ath10k_htt_tx_inc_pending > > This commit removes the call to ath10k_mac_tx_lock() from > ath10k_htt_tx_inc_pending() in case the high water mark is reached. > > ath10k_mac_tx_lock() calls ieee80211_stop_queues() in order to stop > mac80211 from pushing more TX data to the driver (this is the TX lock). > > If a driver is trying to fetch an skb from a queue while the queue is > stopped, ieee80211_tx_dequeue() will return NULL. > > So, in ath10k_mac_tx_push_txq(), there is a risk that the call to > ath10k_htt_tx_inc_pending() results in a stop of the mac80211 TX queues > just before the skb is fetched. > > This will cause ieee80211_tx_dequeue() to return NULL and > ath10k_mac_tx_push_txq() to exit prematurely and return -ENOENT. > Before the function returns ath10k_htt_tx_dec_pending() will be called. > This call will re-enable the TX queues through ath10k_mac_tx_unlock(). > When ath10k_mac_tx_push_txq() has returned, the TX queue will be > returned back to mac80211 with ieee80211_return_txq() without the skb > being properly consumed. > > Since the TX queues were re-enabled in the error exit path of > ath10k_mac_tx_push_txq(), mac80211 can continue pushing data to the > driver. If the hardware does not consume the data, the above mentioned > case will be repeated over and over. > > A case when the hardware is not able to transmit the data from the host > is when a STA has been dis-associated from an AP and has not yet been > able to re-associate. In this case there will be no TX_COMPL_INDs from > the hardware, resulting in the TX counter not be decremented. > > This phenomenon has been observed in both a real and a test setup. > > In order to fix this, the actual TX locking (the call to > ath10k_mac_tx_lock()) was removed from ath10k_htt_tx_inc_pending(). > Instead, ath10k_mac_tx_lock() is called separately after the skb has > been fetched (after the call to ieee80211_tx_dequeue()). At this point > it is OK to stop the queues. Is this patch will impact throughput? > > > _______________________________________________ > ath10k mailing list > ath10k@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/ath10k
