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>

1 files changed, 4 insertions, 12 deletions

diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 271c89bdf049..31494f335686 100644
--- 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)