llc: use a device based hash table to speed up multicast delivery

This patch adds a per SAP device based hash table to solve the
multicast delivery scalability issue when we have large number of
interfaces and a large number of sockets bound to the same SAP.

Signed-off-by: Octavian Purdila <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/llc.h

···
 #define LLC_SAP_STATE_INACTIVE	1
 #define LLC_SAP_STATE_ACTIVE	2
 
+#define LLC_SK_DEV_HASH_BITS 6
+#define LLC_SK_DEV_HASH_ENTRIES (1<<LLC_SK_DEV_HASH_BITS)
+
 /**
  * struct llc_sap - Defines the SAP component
  *
···
 	struct list_head node;
 	spinlock_t sk_lock;
 	struct hlist_nulls_head sk_list;
+	struct hlist_head sk_dev_hash[LLC_SK_DEV_HASH_ENTRIES];
 };
+
+static inline
+struct hlist_head *llc_sk_dev_hash(struct llc_sap *sap, int ifindex)
+{
+	return &sap->sk_dev_hash[ifindex % LLC_SK_DEV_HASH_ENTRIES];
+}
+
 
 #define LLC_DEST_INVALID         0      /* Invalid LLC PDU type */
 #define LLC_DEST_SAP             1      /* Type 1 goes here */

include/net/llc_conn.h

···
 					      received and caused sending FRMR.
 					      Used for resending FRMR */
 	u32		    cmsg_flags;
+	struct hlist_node   dev_hash_node;
 };
 
 static inline struct llc_sock *llc_sk(const struct sock *sk)

net/llc/llc_conn.c

···
  */
 void llc_sap_add_socket(struct llc_sap *sap, struct sock *sk)
 {
+	struct llc_sock *llc = llc_sk(sk);
+	struct hlist_head *dev_hb = llc_sk_dev_hash(sap, llc->dev->ifindex);
+
 	llc_sap_hold(sap);
-	spin_lock_bh(&sap->sk_lock);
 	llc_sk(sk)->sap = sap;
+
+	spin_lock_bh(&sap->sk_lock);
 	sk_nulls_add_node_rcu(sk, &sap->sk_list);
+	hlist_add_head(&llc->dev_hash_node, dev_hb);
 	spin_unlock_bh(&sap->sk_lock);
 }
 
···
  */
 void llc_sap_remove_socket(struct llc_sap *sap, struct sock *sk)
 {
+	struct llc_sock *llc = llc_sk(sk);
+
 	spin_lock_bh(&sap->sk_lock);
 	sk_nulls_del_node_init_rcu(sk);
+	hlist_del(&llc->dev_hash_node);
 	spin_unlock_bh(&sap->sk_lock);
 	llc_sap_put(sap);
 }

net/llc/llc_sap.c

···
 {
 	int i = 0, count = 256 / sizeof(struct sock *);
 	struct sock *sk, *stack[count];
-	struct hlist_nulls_node *node;
+	struct hlist_node *node;
+	struct llc_sock *llc;
+	struct hlist_head *dev_hb = llc_sk_dev_hash(sap, skb->dev->ifindex);
 
 	spin_lock_bh(&sap->sk_lock);
-	sk_nulls_for_each_rcu(sk, node, &sap->sk_list) {
+	hlist_for_each_entry(llc, node, dev_hb, dev_hash_node) {
+
+		sk = &llc->sk;
 
 		if (!llc_mcast_match(sap, laddr, skb, sk))
 			continue;