From:   Erik Stromdahl <erik.stromdahl@gmail.com>
To:     kvalo@qca.qualcomm.com, linux-wireless@vger.kernel.org,
        ath10k@lists.infradead.org
Cc:     yiboz@codeaurora.org, Erik Stromdahl <erik.stromdahl@gmail.com>
Subject: [PATCH] ath10k: remove iteration in wake_tx_queue
Date:   Wed, 27 Mar 2019 17:29:06 +0100
Message-Id: <20190327162906.6010-1-erik.stromdahl@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-wireless-owner@vger.kernel.org
Precedence: bulk

Iterating the TX queue and thereby dequeuing all available packets in the
queue could result in performance penalties on some SMP systems.

The reason for this is most likely that the per-ac lock (active_txq_lock)
in mac80211 will be held by the CPU iterating the current queue.

This will lock up other CPUs trying to push new messages on the TX
queue.

Instead of iterating the queue we fetch just one packet at the time,
resulting in minimal starvation of the other CPUs.

Reported-by: Yibo Zhao <yiboz@codeaurora.org>
Signed-off-by: Erik Stromdahl <erik.stromdahl@gmail.com>
---
 drivers/net/wireless/ath/ath10k/mac.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/net/wireless/ath/ath10k/mac.c b/drivers/net/wireless/ath/ath10k/mac.c
index b73c23d4ce86..c9e700b844f8 100644
--- a/drivers/net/wireless/ath/ath10k/mac.c
+++ b/drivers/net/wireless/ath/ath10k/mac.c
@@ -4356,7 +4356,6 @@ static void ath10k_mac_op_wake_tx_queue(struct ieee80211_hw *hw,
 					struct ieee80211_txq *txq)
 {
 	struct ath10k *ar = hw->priv;
-	int ret;
 	u8 ac;
 
 	ath10k_htt_tx_txq_update(hw, txq);
@@ -4369,11 +4368,9 @@ static void ath10k_mac_op_wake_tx_queue(struct ieee80211_hw *hw,
 	if (!txq)
 		goto out;
 
-	while (ath10k_mac_tx_can_push(hw, txq)) {
-		ret = ath10k_mac_tx_push_txq(hw, txq);
-		if (ret < 0)
-			break;
-	}
+	if (ath10k_mac_tx_can_push(hw, txq))
+		ath10k_mac_tx_push_txq(hw, txq);
+
 	ieee80211_return_txq(hw, txq);
 	ath10k_htt_tx_txq_update(hw, txq);
 out:
-- 
2.19.1