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authorAlexander Duyck <alexander.h.duyck@redhat.com>2015-01-22 15:51:08 -0800
committerDavid S. Miller <davem@davemloft.net>2015-01-25 14:47:15 -0800
commitb3832117b4b61374fac08692f1b1a620088342dd (patch)
tree836e0e535f9fb38c60808b21851923ff3d2744e2 /net/ipv4/fib_trie.c
parentbc579ae5f902e7a17d4a02ca32779c90604d57b9 (diff)
downloadop-kernel-dev-b3832117b4b61374fac08692f1b1a620088342dd.zip
op-kernel-dev-b3832117b4b61374fac08692f1b1a620088342dd.tar.gz
fib_trie: Use index & (~0ul << n->bits) instead of index >> n->bits
In doing performance testing and analysis of the changes I recently found that by shifting the index I had created an unnecessary dependency. I have updated the code so that we instead shift a mask by bits and then just test against that as that should save us about 2 CPU cycles since we can generate the mask while the key and pos are being processed. Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/fib_trie.c')
-rw-r--r--net/ipv4/fib_trie.c16
1 files changed, 8 insertions, 8 deletions
diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 281e5e0..dea2f80 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -961,12 +961,12 @@ static struct tnode *fib_find_node(struct trie *t, u32 key)
* prefix plus zeros for the bits in the cindex. The index
* is the difference between the key and this value. From
* this we can actually derive several pieces of data.
- * if !(index >> bits)
- * we know the value is cindex
- * else
+ * if (index & (~0ul << bits))
* we have a mismatch in skip bits and failed
+ * else
+ * we know the value is cindex
*/
- if (index >> n->bits)
+ if (index & (~0ul << n->bits))
return NULL;
/* we have found a leaf. Prefixes have already been compared */
@@ -1301,12 +1301,12 @@ int fib_table_lookup(struct fib_table *tb, const struct flowi4 *flp,
* prefix plus zeros for the "bits" in the prefix. The index
* is the difference between the key and this value. From
* this we can actually derive several pieces of data.
- * if !(index >> bits)
- * we know the value is child index
- * else
+ * if (index & (~0ul << bits))
* we have a mismatch in skip bits and failed
+ * else
+ * we know the value is cindex
*/
- if (index >> n->bits)
+ if (index & (~0ul << n->bits))
break;
/* we have found a leaf. Prefixes have already been compared */
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