Re: [PATCH 12/12] ath11k: avoid unnecessary lock contention in tx_completion path

On 2021-06-29 23:05, Felix Fietkau wrote:

On 2021-06-15 23:14, Jouni Malinen wrote:

quoted

From: P Praneesh <redacted>

Lock is not needed for the readable idr operation, so avoid 
spin_lock_bh
for the idr_find() call. No need to disable the bottom half preempt if
it is already in bottom half context, so modify the spin_lock_bh to
spin_lock in the data tx completion handler.

Tested-on: IPQ8074 hw2.0 AHB 
WLAN.HK.2.4.0.1-01734-QCAHKSWPL_SILICONZ-1 v2

Co-developed-by: Karthikeyan Periyasamy <redacted>
Signed-off-by: Karthikeyan Periyasamy <redacted>
Signed-off-by: P Praneesh <redacted>
Signed-off-by: Jouni Malinen <redacted>
---
 drivers/net/wireless/ath/ath11k/dp_tx.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/drivers/net/wireless/ath/ath11k/dp_tx.c 

b/drivers/net/wireless/ath/ath11k/dp_tx.c
index ab9ccf0eb274..659f9d98bc0c 100644

--- a/drivers/net/wireless/ath/ath11k/dp_tx.c
+++ b/drivers/net/wireless/ath/ath11k/dp_tx.c

@@ -288,19 +288,18 @@ static void ath11k_dp_tx_free_txbuf(struct 

ath11k_base *ab, u8 mac_id,
 	struct sk_buff *msdu;
 	struct ath11k_skb_cb *skb_cb;

-	spin_lock_bh(&tx_ring->tx_idr_lock);
 	msdu = idr_find(&tx_ring->txbuf_idr, msdu_id);
-	if (!msdu) {
+	if (unlikely(!msdu)) {
 		ath11k_warn(ab, "tx completion for unknown msdu_id %d\n",
 			    msdu_id);
-		spin_unlock_bh(&tx_ring->tx_idr_lock);
 		return;
 	}

 	skb_cb = ATH11K_SKB_CB(msdu);

+	spin_lock(&tx_ring->tx_idr_lock);
 	idr_remove(&tx_ring->txbuf_idr, msdu_id);

Why are you doing the lookups twice instead of just using the return
value of idr_remove?

- Felix

Yes, we will address this in the next version of the patch.