ipv4: speedup inet_dump_ifaddr()

Stephen Hemminger a écrit :
> On Thu, 12 Nov 2009 15:11:36 +0100
> Eric Dumazet <eric.dumazet@gmail.com> wrote:
>
>> When handling large number of netdevices, inet_dump_ifaddr()
>> is very slow because it has O(N^2) complexity.
>>
>> Instead of scanning one single list, we can use the NETDEV_HASHENTRIES
>> sub lists of the dev_index hash table, and RCU lookups.
>>
>> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
>
> You might be able to make RCU critical section smaller by moving
> it into loop.
>

Indeed. But we dump at most one skb (<= 8192 bytes ?), so rcu_read_lock
holding time is small, unless we meet many netdevices without
addresses. I wonder if its really common...

Thanks

[PATCH net-next-2.6] ipv4: speedup inet_dump_ifaddr()

When handling large number of netdevices, inet_dump_ifaddr()
is very slow because it has O(N2) complexity.

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

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

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index c2045f9..7620382 100644 (file)
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1174,39 +1174,54 @@ nla_put_failure:
 static int inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
 {
        struct net *net = sock_net(skb->sk);
-       int idx, ip_idx;
+       int h, s_h;
+       int idx, s_idx;
+       int ip_idx, s_ip_idx;
        struct net_device *dev;
        struct in_device *in_dev;
        struct in_ifaddr *ifa;
-       int s_ip_idx, s_idx = cb->args[0];
+       struct hlist_head *head;
+       struct hlist_node *node;
 
-       s_ip_idx = ip_idx = cb->args[1];
-       idx = 0;
-       for_each_netdev(net, dev) {
-               if (idx < s_idx)
-                       goto cont;
-               if (idx > s_idx)
-                       s_ip_idx = 0;
-               in_dev = __in_dev_get_rtnl(dev);
-               if (!in_dev)
-                       goto cont;
+       s_h = cb->args[0];
+       s_idx = idx = cb->args[1];
+       s_ip_idx = ip_idx = cb->args[2];
 
-               for (ifa = in_dev->ifa_list, ip_idx = 0; ifa;
-                    ifa = ifa->ifa_next, ip_idx++) {
-                       if (ip_idx < s_ip_idx)
-                               continue;
-                       if (inet_fill_ifaddr(skb, ifa, NETLINK_CB(cb->skb).pid,
+       for (h = s_h; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
+               idx = 0;
+               head = &net->dev_index_head[h];
+               rcu_read_lock();
+               hlist_for_each_entry_rcu(dev, node, head, index_hlist) {
+                       if (idx < s_idx)
+                               goto cont;
+                       if (idx > s_idx)
+                               s_ip_idx = 0;
+                       in_dev = __in_dev_get_rcu(dev);
+                       if (!in_dev)
+                               goto cont;
+
+                       for (ifa = in_dev->ifa_list, ip_idx = 0; ifa;
+                            ifa = ifa->ifa_next, ip_idx++) {
+                               if (ip_idx < s_ip_idx)
+                                       continue;
+                               if (inet_fill_ifaddr(skb, ifa,
+                                            NETLINK_CB(cb->skb).pid,
                                             cb->nlh->nlmsg_seq,
-                                            RTM_NEWADDR, NLM_F_MULTI) <= 0)
-                               goto done;
-               }
+                                            RTM_NEWADDR, NLM_F_MULTI) <= 0) {
+                                       rcu_read_unlock();
+                                       goto done;
+                               }
+                       }
 cont:
-               idx++;
+                       idx++;
+               }
+               rcu_read_unlock();
        }
 
 done:
-       cb->args[0] = idx;
-       cb->args[1] = ip_idx;
+       cb->args[0] = h;
+       cb->args[1] = idx;
+       cb->args[2] = ip_idx;
 
        return skb->len;
 }