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>

1 files changed, 2 insertions, 5 deletions

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 */