net: inet_add_protocol() can use cmpxchg()

Use cmpxchg() to get rid of spinlocks in inet_add_protocol() and friends. inet_protos[] & inet6_protos[] are moved to read_mostly section Signed-off-by: Eric Dumazet <[email protected]> Signed-off-by: David S. Miller <[email protected]>
kyagi · Sep 9, 2010 · e038600 · e038600
1 parent 92e32ea
commit e038600
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Showing 2 changed files with 9 additions and 54 deletions.
diff --git a/net/ipv4/protocol.c b/net/ipv4/protocol.c
@@ -28,29 +28,17 @@
 #include <linux/spinlock.h>
 #include <net/protocol.h>
 
-const struct net_protocol *inet_protos[MAX_INET_PROTOS] ____cacheline_aligned_in_smp;
-static DEFINE_SPINLOCK(inet_proto_lock);
+const struct net_protocol *inet_protos[MAX_INET_PROTOS] __read_mostly;
 
 /*
  *	Add a protocol handler to the hash tables
  */
 
 int inet_add_protocol(const struct net_protocol *prot, unsigned char protocol)
 {
-	int hash, ret;
+	int hash = protocol & (MAX_INET_PROTOS - 1);
 
-	hash = protocol & (MAX_INET_PROTOS - 1);
-
-	spin_lock_bh(&inet_proto_lock);
-	if (inet_protos[hash]) {
-		ret = -1;
-	} else {
-		inet_protos[hash] = prot;
-		ret = 0;
-	}
-	spin_unlock_bh(&inet_proto_lock);
-
-	return ret;
+	return !cmpxchg(&inet_protos[hash], NULL, prot) ? 0 : -1;
 }
 EXPORT_SYMBOL(inet_add_protocol);
 
@@ -60,18 +48,9 @@ EXPORT_SYMBOL(inet_add_protocol);
 
 int inet_del_protocol(const struct net_protocol *prot, unsigned char protocol)
 {
-	int hash, ret;
-
-	hash = protocol & (MAX_INET_PROTOS - 1);
+	int ret, hash = protocol & (MAX_INET_PROTOS - 1);
 
-	spin_lock_bh(&inet_proto_lock);
-	if (inet_protos[hash] == prot) {
-		inet_protos[hash] = NULL;
-		ret = 0;
-	} else {
-		ret = -1;
-	}
-	spin_unlock_bh(&inet_proto_lock);
+	ret = (cmpxchg(&inet_protos[hash], prot, NULL) == prot) ? 0 : -1;
 
 	synchronize_net();
 

diff --git a/net/ipv6/protocol.c b/net/ipv6/protocol.c
@@ -25,28 +25,14 @@
 #include <linux/spinlock.h>
 #include <net/protocol.h>
 
-const struct inet6_protocol *inet6_protos[MAX_INET_PROTOS];
-static DEFINE_SPINLOCK(inet6_proto_lock);
-
+const struct inet6_protocol *inet6_protos[MAX_INET_PROTOS] __read_mostly;
 
 int inet6_add_protocol(const struct inet6_protocol *prot, unsigned char protocol)
 {
-	int ret, hash = protocol & (MAX_INET_PROTOS - 1);
-
-	spin_lock_bh(&inet6_proto_lock);
-
-	if (inet6_protos[hash]) {
-		ret = -1;
-	} else {
-		inet6_protos[hash] = prot;
-		ret = 0;
-	}
-
-	spin_unlock_bh(&inet6_proto_lock);
+	int hash = protocol & (MAX_INET_PROTOS - 1);
 
-	return ret;
+	return !cmpxchg(&inet6_protos[hash], NULL, prot) ? 0 : -1;
 }
-
 EXPORT_SYMBOL(inet6_add_protocol);
 
 /*
@@ -57,20 +43,10 @@ int inet6_del_protocol(const struct inet6_protocol *prot, unsigned char protocol
 {
 	int ret, hash = protocol & (MAX_INET_PROTOS - 1);
 
-	spin_lock_bh(&inet6_proto_lock);
-
-	if (inet6_protos[hash] != prot) {
-		ret = -1;
-	} else {
-		inet6_protos[hash] = NULL;
-		ret = 0;
-	}
-
-	spin_unlock_bh(&inet6_proto_lock);
+	ret = (cmpxchg(&inet6_protos[hash], prot, NULL) == prot) ? 0 : -1;
 
 	synchronize_net();
 
 	return ret;
 }
-
 EXPORT_SYMBOL(inet6_del_protocol);