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>

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 6994101..0addd45 100644 (file)
--- 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 fa88dcd..e7bada1 100644 (file)
--- 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 ba13b09..52ea418 100644 (file)
--- 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;
 }