net: Use static_key for XPS maps

Use static_key for XPS maps to reduce the cost of extra map checks,
similar to how it is used for RPS and RFS. This includes static_key
'xps_needed' for XPS and another for 'xps_rxqs_needed' for XPS using
Rx queues map.

Signed-off-by: Amritha Nambiar <amritha.nambiar@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -2081,6 +2081,10 @@ int netdev_txq_to_tc(struct net_device *dev, unsigned int txq)
 EXPORT_SYMBOL(netdev_txq_to_tc);
 
 #ifdef CONFIG_XPS
+struct static_key xps_needed __read_mostly;
+EXPORT_SYMBOL(xps_needed);
+struct static_key xps_rxqs_needed __read_mostly;
+EXPORT_SYMBOL(xps_rxqs_needed);
 static DEFINE_MUTEX(xps_map_mutex);
 #define xmap_dereference(P)		\
 	rcu_dereference_protected((P), lockdep_is_held(&xps_map_mutex))
@@ -2168,14 +2172,18 @@ static void netif_reset_xps_queues(struct net_device *dev, u16 offset,
 	struct xps_dev_maps *dev_maps;
 	unsigned int nr_ids;
 
-	mutex_lock(&xps_map_mutex);
+	if (!static_key_false(&xps_needed))
+		return;
 
-	dev_maps = xmap_dereference(dev->xps_rxqs_map);
-	if (dev_maps) {
-		nr_ids = dev->num_rx_queues;
-		clean_xps_maps(dev, possible_mask, dev_maps, nr_ids, offset,
-			       count, true);
+	mutex_lock(&xps_map_mutex);
 
+	if (static_key_false(&xps_rxqs_needed)) {
+		dev_maps = xmap_dereference(dev->xps_rxqs_map);
+		if (dev_maps) {
+			nr_ids = dev->num_rx_queues;
+			clean_xps_maps(dev, possible_mask, dev_maps, nr_ids,
+				       offset, count, true);
+		}
 	}
 
 	dev_maps = xmap_dereference(dev->xps_cpus_map);
@@ -2189,6 +2197,10 @@ static void netif_reset_xps_queues(struct net_device *dev, u16 offset,
 		       false);
 
 out_no_maps:
+	if (static_key_enabled(&xps_rxqs_needed))
+		static_key_slow_dec(&xps_rxqs_needed);
+
+	static_key_slow_dec(&xps_needed);
 	mutex_unlock(&xps_map_mutex);
 }
 
@@ -2297,6 +2309,10 @@ int __netif_set_xps_queue(struct net_device *dev, const unsigned long *mask,
 	if (!new_dev_maps)
 		goto out_no_new_maps;
 
+	static_key_slow_inc(&xps_needed);
+	if (is_rxqs_map)
+		static_key_slow_inc(&xps_rxqs_needed);
+
 	for (j = -1; j = netif_attrmask_next(j, possible_mask, nr_ids),
 	     j < nr_ids;) {
 		/* copy maps belonging to foreign traffic classes */
@@ -3450,6 +3466,9 @@ static inline int get_xps_queue(struct net_device *dev, struct sk_buff *skb)
 	struct xps_map *map;
 	int queue_index = -1;
 
+	if (!static_key_false(&xps_needed))
+		return -1;
+
 	rcu_read_lock();
 	dev_maps = rcu_dereference(dev->xps_cpus_map);
 	if (dev_maps) {