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>

net/ipv4/devinet.c

@@ -1174,20 +1174,29 @@ static int inet_fill_ifaddr(struct sk_buff *skb, struct in_ifaddr *ifa,
 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];
+	s_h = cb->args[0];
+	s_idx = idx = cb->args[1];
+	s_ip_idx = ip_idx = cb->args[2];
+
+	for (h = s_h; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
 		idx = 0;
-	for_each_netdev(net, dev) {
+		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_rtnl(dev);
+			in_dev = __in_dev_get_rcu(dev);
 			if (!in_dev)
 				goto cont;
 
@@ -1195,18 +1204,24 @@ static int inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
 			     ifa = ifa->ifa_next, ip_idx++) {
 				if (ip_idx < s_ip_idx)
 					continue;
-			if (inet_fill_ifaddr(skb, ifa, NETLINK_CB(cb->skb).pid,
+				if (inet_fill_ifaddr(skb, ifa,
+					     NETLINK_CB(cb->skb).pid,
 					     cb->nlh->nlmsg_seq,
-					     RTM_NEWADDR, NLM_F_MULTI) <= 0)
+					     RTM_NEWADDR, NLM_F_MULTI) <= 0) {
+					rcu_read_unlock();
 					goto done;
 				}
+			}
 cont:
 			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;
 }