ipv6: speedup inet6_dump_ifinfo()

When handling large number of netdevice, inet6_dump_ifinfo()
is very slow because it has O(N^2) complexity.

Instead of scanning one single list, we can use the 256 sub lists
of the dev_index hash table, and RCU lookups.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 024bba3..f9f7fd6 100644 (file)
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -3823,28 +3823,39 @@ nla_put_failure:
 static int inet6_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 {
        struct net *net = sock_net(skb->sk);
-       int idx, err;
-       int s_idx = cb->args[0];
+       int h, s_h;
+       int idx = 0, err, s_idx;
        struct net_device *dev;
        struct inet6_dev *idev;
+       struct hlist_head *head;
+       struct hlist_node *node;
 
-       read_lock(&dev_base_lock);
-       idx = 0;
-       for_each_netdev(net, dev) {
-               if (idx < s_idx)
-                       goto cont;
-               if ((idev = in6_dev_get(dev)) == NULL)
-                       goto cont;
-               err = inet6_fill_ifinfo(skb, idev, NETLINK_CB(cb->skb).pid,
-                               cb->nlh->nlmsg_seq, RTM_NEWLINK, NLM_F_MULTI);
-               in6_dev_put(idev);
-               if (err <= 0)
-                       break;
+       s_h = cb->args[0];
+       s_idx = cb->args[1];
+
+       rcu_read_lock();
+       for (h = s_h; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
+               idx = 0;
+               head = &net->dev_index_head[h];
+               hlist_for_each_entry_rcu(dev, node, head, index_hlist) {
+                       if (idx < s_idx)
+                               goto cont;
+                       idev = __in6_dev_get(dev);
+                       if (!idev)
+                               goto cont;
+                       if (inet6_fill_ifinfo(skb, idev,
+                                             NETLINK_CB(cb->skb).pid,
+                                             cb->nlh->nlmsg_seq,
+                                             RTM_NEWLINK, NLM_F_MULTI) <= 0)
+                               goto out;
 cont:
-               idx++;
+                       idx++;
+               }
        }
-       read_unlock(&dev_base_lock);
-       cb->args[0] = idx;
+out:
+       rcu_read_unlock();
+       cb->args[1] = idx;
+       cb->args[0] = h;
 
        return skb->len;
 }