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

[P Praneesh]

On 2021-06-29 23:05, Felix Fietkau wrote:
> On 2021-06-15 23:14, Jouni Malinen wrote:
>> From: P Praneesh <ppranees at codeaurora.org>
>> 
>> 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 <periyasa at codeaurora.org>
>> Signed-off-by: Karthikeyan Periyasamy <periyasa at codeaurora.org>
>> Signed-off-by: P Praneesh <ppranees at codeaurora.org>
>> Signed-off-by: Jouni Malinen <jouni at codeaurora.org>
>> ---
>>  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.