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>

1 files changed, 38 insertions, 23 deletions

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index c2045f9615da..7620382058a0 100644
--- 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;
 }