ipv6: optimize link local address search

ipv6_link_dev_addr sorts newly added addresses by scope in
ifp->addr_list. Smaller scope addresses are added to the tail of the
list. Use this fact to iterate in reverse over addr_list and break out
as soon as a higher scoped one showes up, so we can spare some cycles
on machines with lot's of addresses.

The ordering of the addresses is not relevant and we are more likely to
get the eui64 generated address with this change anyway.
Suggested-by: NBrian Haley <brian.haley@hp.com>
Signed-off-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -1437,7 +1437,9 @@ int __ipv6_get_lladdr(struct inet6_dev *idev, struct in6_addr *addr,
 	struct inet6_ifaddr *ifp;
 	int err = -EADDRNOTAVAIL;
 
-	list_for_each_entry(ifp, &idev->addr_list, if_list) {
+	list_for_each_entry_reverse(ifp, &idev->addr_list, if_list) {
+		if (ifp->scope > IFA_LINK)
+			break;
 		if (ifp->scope == IFA_LINK &&
 		    !(ifp->flags & banned_flags)) {
 			*addr = ifp->addr;
@@ -1858,7 +1860,9 @@ static int ipv6_inherit_eui64(u8 *eui, struct inet6_dev *idev)
 	struct inet6_ifaddr *ifp;
 
 	read_lock_bh(&idev->lock);
-	list_for_each_entry(ifp, &idev->addr_list, if_list) {
+	list_for_each_entry_reverse(ifp, &idev->addr_list, if_list) {
+		if (ifp->scope > IFA_LINK)
+			break;
 		if (ifp->scope == IFA_LINK && !(ifp->flags&IFA_F_TENTATIVE)) {
 			memcpy(eui, ifp->addr.s6_addr+8, 8);
 			err = 0;
@@ -3239,7 +3243,9 @@ static bool ipv6_lonely_lladdr(struct inet6_ifaddr *ifp)
 	struct inet6_ifaddr *ifpiter;
 	struct inet6_dev *idev = ifp->idev;
 
-	list_for_each_entry(ifpiter, &idev->addr_list, if_list) {
+	list_for_each_entry_reverse(ifpiter, &idev->addr_list, if_list) {
+		if (ifpiter->scope > IFA_LINK)
+			break;
 		if (ifp != ifpiter && ifpiter->scope == IFA_LINK &&
 		    (ifpiter->flags & (IFA_F_PERMANENT|IFA_F_TENTATIVE|
 				       IFA_F_OPTIMISTIC|IFA_F_DADFAILED)) ==