qcacmn: Restrict length of pdev backpressure event list

In current architecture, when host receives backpressure
event from FW, it prints pdev_id, ring_id, hp and tp values
for that ring in the tasklet context.
In same context, memory to hold the information of other
rings is allocate,  which then put into the list maintained
at pdev level and work is scheduled for printing this info.

In scenarios of heavy load, where the backpressure events
are continuously triggered, the list can grow to a bigger
one and printing of ring stats for all of these events can
be a heavy CPU hit.

As an optimization, restrict the depth of the list to 16
by checking the size of list when backpressure event is
received from FW. When list size reaches the max value (16),
then remove the entry from head and insert the new entry at tail.

Also in the worker thread, fetch only 1 entry from the list for
printing and schedule the work again if the list is not empty.

Change-Id: If4291b9d5ebee1e3d1eea80bbd0134faf090b2b8
CRs-Fixed: 3049635

dp/wifi3.0/dp_htt.c

@@ -57,6 +57,8 @@
 	((pkt->htc_pkt.Status != QDF_STATUS_E_CANCELED) && \
 	(pkt->htc_pkt.Status != QDF_STATUS_E_RESOURCES))
 
+#define HTT_BKP_STATS_MAX_QUEUE_DEPTH 16
+
 /*
  * htt_htc_pkt_alloc() - Allocate HTC packet buffer
  * @htt_soc:	HTT SOC handle
@@ -2229,6 +2231,7 @@ static void dp_queue_ring_stats(struct dp_pdev *pdev)
 	int lmac_id;
 	uint32_t j = 0;
 	struct dp_soc_srngs_state * soc_srngs_state = NULL;
+	struct dp_soc_srngs_state *drop_srngs_state = NULL;
 	QDF_STATUS status;
 
 	soc_srngs_state = qdf_mem_malloc(sizeof(struct dp_soc_srngs_state));
@@ -2410,6 +2413,17 @@ static void dp_queue_ring_stats(struct dp_pdev *pdev)
 	qdf_spin_lock_bh(&pdev->bkp_stats.list_lock);
 
 	soc_srngs_state->seq_num = pdev->bkp_stats.seq_num;
+
+	if (pdev->bkp_stats.queue_depth >= HTT_BKP_STATS_MAX_QUEUE_DEPTH) {
+		drop_srngs_state = TAILQ_FIRST(&pdev->bkp_stats.list);
+		qdf_assert_always(drop_srngs_state);
+		TAILQ_REMOVE(&pdev->bkp_stats.list, drop_srngs_state,
+			     list_elem);
+		qdf_mem_free(drop_srngs_state);
+		pdev->bkp_stats.queue_depth--;
+	}
+
+	pdev->bkp_stats.queue_depth++;
 	TAILQ_INSERT_TAIL(&pdev->bkp_stats.list, soc_srngs_state,
 			  list_elem);
 	pdev->bkp_stats.seq_num++;
@@ -3833,25 +3847,28 @@ dp_htt_rx_fisa_config(struct dp_pdev *pdev,
 static void dp_bk_pressure_stats_handler(void *context)
 {
 	struct dp_pdev *pdev = (struct dp_pdev *)context;
-	struct dp_soc_srngs_state *soc_srngs_state, *soc_srngs_state_next;
+	struct dp_soc_srngs_state *soc_srngs_state = NULL;
 	const char *ring_name;
 	int i;
 	struct dp_srng_ring_state *ring_state;
+	bool empty_flag;
 
-	TAILQ_HEAD(, dp_soc_srngs_state) soc_srngs_state_list;
-
-	TAILQ_INIT(&soc_srngs_state_list);
 	qdf_spin_lock_bh(&pdev->bkp_stats.list_lock);
-	TAILQ_CONCAT(&soc_srngs_state_list, &pdev->bkp_stats.list,
-		     list_elem);
-	qdf_spin_unlock_bh(&pdev->bkp_stats.list_lock);
 
-	TAILQ_FOREACH_SAFE(soc_srngs_state, &soc_srngs_state_list,
-			   list_elem, soc_srngs_state_next) {
-		TAILQ_REMOVE(&soc_srngs_state_list, soc_srngs_state,
+	/* Extract only first entry for printing in one work event */
+	if (pdev->bkp_stats.queue_depth &&
+	    !TAILQ_EMPTY(&pdev->bkp_stats.list)) {
+		soc_srngs_state = TAILQ_FIRST(&pdev->bkp_stats.list);
+		TAILQ_REMOVE(&pdev->bkp_stats.list, soc_srngs_state,
 			     list_elem);
+		pdev->bkp_stats.queue_depth--;
+	}
 
-		DP_PRINT_STATS("### START BKP stats for seq_num %u ###",
+	empty_flag = TAILQ_EMPTY(&pdev->bkp_stats.list);
+	qdf_spin_unlock_bh(&pdev->bkp_stats.list_lock);
+
+	if (soc_srngs_state) {
+		DP_PRINT_STATS("### BKP stats for seq_num %u START ###",
 			       soc_srngs_state->seq_num);
 		for (i = 0; i < soc_srngs_state->max_ring_id; i++) {
 			ring_state = &soc_srngs_state->ring_state[i];
@@ -3873,6 +3890,11 @@ static void dp_bk_pressure_stats_handler(void *context)
 		qdf_mem_free(soc_srngs_state);
 	}
 	dp_print_napi_stats(pdev->soc);
+
+	/* Schedule work again if queue is not empty */
+	if (!empty_flag)
+		qdf_queue_work(0, pdev->bkp_stats.work_queue,
+			       &pdev->bkp_stats.work);
 }
 
 /*
@@ -3915,6 +3937,7 @@ QDF_STATUS dp_pdev_bkp_stats_attach(struct dp_pdev *pdev)
 {
 	TAILQ_INIT(&pdev->bkp_stats.list);
 	pdev->bkp_stats.seq_num = 0;
+	pdev->bkp_stats.queue_depth = 0;
 
 	qdf_create_work(0, &pdev->bkp_stats.work,
 			dp_bk_pressure_stats_handler, pdev);

dp/wifi3.0/dp_types.h

@@ -2657,6 +2657,7 @@ struct dp_pdev {
 		qdf_work_t work;
 		qdf_workqueue_t *work_queue;
 		uint32_t seq_num;
+		uint8_t queue_depth;
 		qdf_spinlock_t list_lock;
 
 		TAILQ_HEAD(, dp_soc_srngs_state) list;