wifi: ath12k: Optimize the lock contention of used list in Rx data path

When a packet arrives in Rx rings, the RX descriptor moves from the used
list to the free list. Then, the rxdma ring gets replenished, where the Rx
descriptor again moves from the free list to the used list. At the end, the
descriptor came to the used list with unnecessary list movement. The
descriptor used list is maintained in the Rxdma ring structure, which
creates lock contention for the list operations (add, delete) in the Rx
data path. Optimize the Rx data path by removing the used list from the
common Rxdma ring and maintain as a local variable in the Rx ring handler
itself, which avoid lock contention. Now, to find the used list descriptor
during descriptor cleanup, we need to check the in_use flag for each Rx
descriptor.

This is a simple UDP UL throughput test case results on x86+NUC device
with QCN9274 card, which clearly shows 8% to 12% improvement in the CPU
idle for the same ingress traffic.

Before:
Average:     CPU    %usr   %nice    %sys %iowait    %irq   %soft  %steal  %guest  %gnice   %idle
Average:     all    0.24    0.00   12.54    0.08    0.00   23.33    0.00    0.00    0.00   63.81

After:
Average:     CPU    %usr   %nice    %sys %iowait    %irq   %soft  %steal  %guest  %gnice   %idle
Average:     all    0.34    0.00    4.60    0.00    0.00   19.59    0.00    0.00    0.00   75.47

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.0.1-00029-QCAHKSWPL_SILICONZ-1

Signed-off-by: Karthikeyan Periyasamy <quic_periyasa@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240320010615.91331-3-quic_periyasa@quicinc.com

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/net/wireless/ath/ath12k/dp.h b/drivers/net/wireless/ath/ath12k/dp.h
index 9b83b9230bbc..443e6af619ef 100644
--- a/drivers/net/wireless/ath/ath12k/dp.h
+++ b/drivers/net/wireless/ath/ath12k/dp.h
@@ -282,6 +282,8 @@ struct ath12k_rx_desc_info {
 	struct sk_buff *skb;
 	u32 cookie;
 	u32 magic;
+	u8 in_use	: 1,
+	   reserved	: 7;
 };
 
 struct ath12k_tx_desc_info {
@@ -347,8 +349,7 @@ struct ath12k_dp {
 	struct ath12k_spt_info *spt_info;
 	u32 num_spt_pages;
 	struct list_head rx_desc_free_list;
-	struct list_head rx_desc_used_list;
-	/* protects the free and used desc list */
+	/* protects the free desc list */
 	spinlock_t rx_desc_lock;
 
 	struct list_head tx_desc_free_list[ATH12K_HW_MAX_QUEUES];