fib_trie: use fls() instead of open coded loop

fib_table_lookup() might use fls() to speedup an open coded loop.

Noticed while doing a profile analysis.

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

diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 271c89b..31494f3 100644 (file)
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -1384,8 +1384,7 @@ int fib_table_lookup(struct fib_table *tb, const struct flowi *flp,
        t_key cindex = 0;
        int current_prefix_length = KEYLENGTH;
        struct tnode *cn;
-       t_key node_prefix, key_prefix, pref_mismatch;
-       int mp;
+       t_key pref_mismatch;
 
        rcu_read_lock();
 
@@ -1500,10 +1499,7 @@ int fib_table_lookup(struct fib_table *tb, const struct flowi *flp,
                 * matching prefix.
                 */
 
-               node_prefix = mask_pfx(cn->key, cn->pos);
-               key_prefix = mask_pfx(key, cn->pos);
-               pref_mismatch = key_prefix^node_prefix;
-               mp = 0;
+               pref_mismatch = mask_pfx(cn->key ^ key, cn->pos);
 
                /*
                 * In short: If skipped bits in this node do not match
@@ -1511,13 +1507,9 @@ int fib_table_lookup(struct fib_table *tb, const struct flowi *flp,
                 * state.directly.
                 */
                if (pref_mismatch) {
-                       while (!(pref_mismatch & (1<<(KEYLENGTH-1)))) {
-                               mp++;
-                               pref_mismatch = pref_mismatch << 1;
-                       }
-                       key_prefix = tkey_extract_bits(cn->key, mp, cn->pos-mp);
+                       int mp = KEYLENGTH - fls(pref_mismatch);
 
-                       if (key_prefix != 0)
+                       if (tkey_extract_bits(cn->key, mp, cn->pos - mp) != 0)
                                goto backtrace;
 
                        if (current_prefix_length >= cn->pos)