rtnetlink: speedup rtnl_dump_ifinfo()

When handling large number of netdevice, rtnl_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.

This considerably speedups "ip link" operations

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

3 files changed, 30 insertions, 18 deletions

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 699410142bfa..0addd45038ac 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -28,6 +28,10 @@ struct ctl_table_header;
 struct net_generic;
 struct sock;
 
+
+#define NETDEV_HASHBITS    8
+#define NETDEV_HASHENTRIES (1 << NETDEV_HASHBITS)
+
 struct net {
         atomic_t                count;          /* To decided when the network
                                                  *  namespace should be freed.
diff --git a/net/core/dev.c b/net/core/dev.c
index fa88dcd476d6..e7bada1d5ed9 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -193,18 +193,15 @@ static struct list_head ptype_all __read_mostly;	/* Taps */
 DEFINE_RWLOCK(dev_base_lock);
 EXPORT_SYMBOL(dev_base_lock);
 
-#define NETDEV_HASHBITS 8
-#define NETDEV_HASHENTRIES (1 << NETDEV_HASHBITS)
-
 static inline struct hlist_head *dev_name_hash(struct net *net, const char *name)
 {
         unsigned hash = full_name_hash(name, strnlen(name, IFNAMSIZ));
-        return &net->dev_name_head[hash & ((1 << NETDEV_HASHBITS) - 1)];
+        return &net->dev_name_head[hash & (NETDEV_HASHENTRIES - 1)];
 }
 
 static inline struct hlist_head *dev_index_hash(struct net *net, int ifindex)
 {
-        return &net->dev_index_head[ifindex & ((1 << NETDEV_HASHBITS) - 1)];
+        return &net->dev_index_head[ifindex & (NETDEV_HASHENTRIES - 1)];
 }
 
 /* Device list insertion */
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index ba13b0974a7b..52ea418d5302 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -682,22 +682,33 @@ nla_put_failure:
 static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 {
         struct net *net = sock_net(skb->sk);
-        int idx;
-        int s_idx = cb->args[0];
+        int h, s_h;
+        int idx = 0, s_idx;
         struct net_device *dev;
-
-        idx = 0;
-        for_each_netdev(net, dev) {
-                if (idx < s_idx)
-                        goto cont;
-                if (rtnl_fill_ifinfo(skb, dev, RTM_NEWLINK,
-                                     NETLINK_CB(cb->skb).pid,
-                                     cb->nlh->nlmsg_seq, 0, NLM_F_MULTI) <= 0)
-                        break;
+        struct hlist_head *head;
+        struct hlist_node *node;
+
+        s_h = cb->args[0];
+        s_idx = cb->args[1];
+
+        for (h = s_h; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
+                idx = 0;
+                head = &net->dev_index_head[h];
+                hlist_for_each_entry(dev, node, head, index_hlist) {
+                        if (idx < s_idx)
+                                goto cont;
+                        if (rtnl_fill_ifinfo(skb, dev, RTM_NEWLINK,
+                                             NETLINK_CB(cb->skb).pid,
+                                             cb->nlh->nlmsg_seq, 0,
+                                             NLM_F_MULTI) <= 0)
+                                goto out;
 cont:
-                idx++;
+                        idx++;
+                }
         }
-        cb->args[0] = idx;
+out:
+        cb->args[1] = idx;
+        cb->args[0] = h;
 
         return skb->len;
 }