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Subject: Re: [PATCH 12/12] ath11k: avoid unnecessary lock contention in
 tx_completion path
To:     Jouni Malinen <jouni@codeaurora.org>,
        Kalle Valo <kvalo@codeaurora.org>
Cc:     ath11k@lists.infradead.org, linux-wireless@vger.kernel.org,
        P Praneesh <ppranees@codeaurora.org>,
        Karthikeyan Periyasamy <periyasa@codeaurora.org>
References: <20210615211407.92233-1-jouni@codeaurora.org>
 <20210615211407.92233-13-jouni@codeaurora.org>
From:   Felix Fietkau <nbd@nbd.name>
Message-ID: <b1dbd11a-e978-16ea-1473-7eb81399981c@nbd.name>
Date:   Tue, 29 Jun 2021 19:35:43 +0200
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On 2021-06-15 23:14, Jouni Malinen wrote:
> From: P Praneesh <ppranees@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@codeaurora.org>
> Signed-off-by: Karthikeyan Periyasamy <periyasa@codeaurora.org>
> Signed-off-by: P Praneesh <ppranees@codeaurora.org>
> Signed-off-by: Jouni Malinen <jouni@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