From 874ffa8f72444d6253d2669fed304875c128f86b Mon Sep 17 00:00:00 2001
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Wed, 13 Oct 2010 06:56:11 +0000
Subject: [PATCH] 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>
---
net/ipv4/fib_trie.c | 16 ++++------------
1 file 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)
--
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