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ipv4: Call fib_select_default() only when actually necessary. 

fib_select_default() is a complete NOP, and completely pointless
to invoke, when we have no more than 1 default route installed.

And this is far and away the common case.

So remember how many prefixlen==0 routes we have in the routing
table, and elide the call when we have no more than one of those.

This cuts output route creation time by 157 cycles on Niagara2+.

In order to add the new int to fib_table, we have to correct the type
of ->tb_data[] to unsigned long, otherwise the private area will be
unaligned on 64-bit systems.

Signed-off-by: David S. Miller <davem@davemloft.net>
Reviewed-by: Eric Dumazet <eric.dumazet@gmail.com>
This commit is contained in:
David S. Miller 2011-04-14 14:49:37 -07:00
parent 8849b720e9
commit 21d8c49e01
3 changed files with 12 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/net/ip_fib.h
View File

@ -160,7 +160,8 @@ struct fib_table {
struct hlist_node tb_hlist;
u32 tb_id;
int tb_default;
unsigned char tb_data[0];
int tb_num_default;
unsigned long tb_data[0];
};
extern int fib_table_lookup(struct fib_table *tb, const struct flowi4 *flp,

7
net/ipv4/fib_trie.c
View File

@ -1332,6 +1332,9 @@ int fib_table_insert(struct fib_table *tb, struct fib_config *cfg)
}
}
if (!plen)
tb->tb_num_default++;
list_add_tail_rcu(&new_fa->fa_list,
(fa ? &fa->fa_list : fa_head));
@ -1697,6 +1700,9 @@ int fib_table_delete(struct fib_table *tb, struct fib_config *cfg)
list_del_rcu(&fa->fa_list);
if (!plen)
tb->tb_num_default--;
if (list_empty(fa_head)) {
hlist_del_rcu(&li->hlist);
free_leaf_info(li);
@ -1987,6 +1993,7 @@ struct fib_table *fib_trie_table(u32 id)
tb->tb_id = id;
tb->tb_default = -1;
tb->tb_num_default = 0;
t = (struct trie *) tb->tb_data;
memset(t, 0, sizeof(*t));

4
net/ipv4/route.c
View File

@ -2615,7 +2615,9 @@ static struct rtable *ip_route_output_slow(struct net *net,
fib_select_multipath(&res);
else
#endif
if (!res.prefixlen && res.type == RTN_UNICAST && !fl4.flowi4_oif)
if (!res.prefixlen &&
res.table->tb_num_default > 1 &&
res.type == RTN_UNICAST && !fl4.flowi4_oif)
fib_select_default(&res);
if (!fl4.saddr)