Bluetooth: host: poll on CTLR buffers instead of host TX queue

When there are no buffers, it doesn't make sense to repeatedly try to
send the host TX queue.

Signed-off-by: Jonathan Rico <jonathan.rico@nordicsemi.no>
(cherry picked from commit ef19c64)

Author: jori-nordic

subsys/bluetooth/host/conn.c

@@ -480,7 +480,7 @@ static int send_frag(struct bt_conn *conn, struct net_buf *buf, uint8_t flags,
 	int err = 0;
 
 	/* Check if the controller can accept ACL packets */
-	if (k_sem_take(bt_conn_get_pkts(conn), K_MSEC(100))) {
+	if (k_sem_take(bt_conn_get_pkts(conn), K_NO_WAIT)) {
 		/* not `goto fail`, we don't want to free the tx context: in the
 		 * case where it is the original buffer, it will contain the
 		 * callback ptr.
@@ -717,10 +717,26 @@ static int conn_prepare_events(struct bt_conn *conn,
 
 	BT_DBG("Adding conn %p to poll list", conn);
 
-	k_poll_event_init(&events[0],
-			K_POLL_TYPE_FIFO_DATA_AVAILABLE,
-			K_POLL_MODE_NOTIFY_ONLY,
-			&conn->tx_queue);
+	bool buffers_available = k_sem_count_get(bt_conn_get_pkts(conn)) > 0;
+	bool packets_waiting = !k_fifo_is_empty(&conn->tx_queue);
+
+	if (packets_waiting && !buffers_available) {
+		/* Only resume sending when the controller has buffer space
+		 * available for this connection.
+		 */
+		BT_DBG("wait on ctlr buffers");
+		k_poll_event_init(&events[0],
+				  K_POLL_TYPE_SEM_AVAILABLE,
+				  K_POLL_MODE_NOTIFY_ONLY,
+				  bt_conn_get_pkts(conn));
+	} else {
+		/* Wait until there is more data to send. */
+		BT_DBG("wait on host fifo");
+		k_poll_event_init(&events[0],
+				  K_POLL_TYPE_FIFO_DATA_AVAILABLE,
+				  K_POLL_MODE_NOTIFY_ONLY,
+				  &conn->tx_queue);
+	}
 	events[0].tag = BT_EVENT_CONN_TX_QUEUE;
 
 	return 0;

subsys/bluetooth/host/hci_core.c

@@ -2372,6 +2372,13 @@ static void process_events(struct k_poll_event *ev, int count)
 		switch (ev->state) {
 		case K_POLL_STATE_SIGNALED:
 			break;
+		case K_POLL_STATE_SEM_AVAILABLE:
+			/* After this fn is exec'd, `bt_conn_prepare_events()`
+			 * will be called once again, and this time buffers will
+			 * be available, so the FIFO will be added to the poll
+			 * list instead of the ctlr buffers semaphore.
+			 */
+			break;
 		case K_POLL_STATE_FIFO_DATA_AVAILABLE:
 			if (ev->tag == BT_EVENT_CMD_TX) {
 				send_cmd();
@@ -2431,6 +2438,7 @@ static void hci_tx_thread(void *p1, void *p2, void *p3)
 		events[0].state = K_POLL_STATE_NOT_READY;
 		ev_count = 1;
 
+		/* This adds the FIFO per-connection */
 		if (IS_ENABLED(CONFIG_BT_CONN) || IS_ENABLED(CONFIG_BT_ISO)) {
 			ev_count += bt_conn_prepare_events(&events[1]);
 		}

tests/bluetooth/bsim_bt/bsim_test_l2cap_stress/src/common.h

@@ -36,7 +36,7 @@ extern enum bst_result_t bst_result;
 	}
 
 
-#define WAIT_SECONDS 120                         /* seconds */
+#define WAIT_SECONDS 270                        /* seconds */
 #define WAIT_TIME (WAIT_SECONDS * USEC_PER_SEC) /* microseconds*/
 
 #define FAIL(...)				       \

tests/bluetooth/bsim_bt/bsim_test_l2cap_stress/tests_scripts/l2cap.sh

@@ -35,7 +35,7 @@ Execute "${bsim_exe}" -v=${verbosity_level} -s=${simulation_id} -d=4 -testid=per
 Execute "${bsim_exe}" -v=${verbosity_level} -s=${simulation_id} -d=5 -testid=peripheral -rs=230
 Execute "${bsim_exe}" -v=${verbosity_level} -s=${simulation_id} -d=6 -testid=peripheral -rs=9
 
-Execute ./bs_2G4_phy_v1 -v=${verbosity_level} -s=${simulation_id} -D=7 -sim_length=240e6 $@
+Execute ./bs_2G4_phy_v1 -v=${verbosity_level} -s=${simulation_id} -D=7 -sim_length=270e6 $@
 
 for process_id in $process_ids; do
   wait $process_id || let "exit_code=$?"