[PATCH] ath10k: Restart xmit queues below low-water mark.

[greearb@candelatech.com]

From: Ben Greear <greearb@candelatech.com>

While running tcp upload + download tests with ~200
concurrent TCP streams, 1-2 processes, and 30 station
vdevs, I noticed that the __ieee80211_stop_queue was taking
around 20% of the CPU according to perf-top, which other locking
taking an additional ~15%.

I believe the issue is that the ath10k driver would unlock the
txqueue when a single frame could be transmitted, instead of
waiting for a low water mark.

So, this patch adds a low-water mark that is 1/4 of the total
tx buffers allowed.

This appears to resolve the performance problem that I saw.

Tested with recent wave-1 ath10k-ct firmware.

Signed-off-by: Ben Greear <greearb@candelatech.com>
---
 drivers/net/wireless/ath/ath10k/htt.h    | 1 +
 drivers/net/wireless/ath/ath10k/htt_tx.c | 8 ++++++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/ath/ath10k/htt.h b/drivers/net/wireless/ath/ath10k/htt.h
index 31c4ddbf45cb..b5634781c0dc 100644
--- a/drivers/net/wireless/ath/ath10k/htt.h
+++ b/drivers/net/wireless/ath/ath10k/htt.h
@@ -1941,6 +1941,7 @@ struct ath10k_htt {
 
 	u8 target_version_major;
 	u8 target_version_minor;
+	bool needs_unlock;
 	struct completion target_version_received;
 	u8 max_num_amsdu;
 	u8 max_num_ampdu;
diff --git a/drivers/net/wireless/ath/ath10k/htt_tx.c b/drivers/net/wireless/ath/ath10k/htt_tx.c
index 9b3c3b080e92..44795d9a7c0c 100644
--- a/drivers/net/wireless/ath/ath10k/htt_tx.c
+++ b/drivers/net/wireless/ath/ath10k/htt_tx.c
@@ -145,8 +145,10 @@ void ath10k_htt_tx_dec_pending(struct ath10k_htt *htt)
 	lockdep_assert_held(&htt->tx_lock);
 
 	htt->num_pending_tx--;
-	if (htt->num_pending_tx == htt->max_num_pending_tx - 1)
+	if ((htt->num_pending_tx <= (htt->max_num_pending_tx / 4)) && htt->needs_unlock) {
+		htt->needs_unlock = false;
 		ath10k_mac_tx_unlock(htt->ar, ATH10K_TX_PAUSE_Q_FULL);
+	}
 }
 
 int ath10k_htt_tx_inc_pending(struct ath10k_htt *htt)
@@ -157,8 +159,10 @@ int ath10k_htt_tx_inc_pending(struct ath10k_htt *htt)
 		return -EBUSY;
 
 	htt->num_pending_tx++;
-	if (htt->num_pending_tx == htt->max_num_pending_tx)
+	if (htt->num_pending_tx == htt->max_num_pending_tx) {
+		htt->needs_unlock = true;
 		ath10k_mac_tx_lock(htt->ar, ATH10K_TX_PAUSE_Q_FULL);
+	}
 
 	return 0;
 }
-- 
2.20.1