You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
53 lines
1.9 KiB
53 lines
1.9 KiB
10 years ago
|
From: Alexander Duyck <alexander.h.duyck@redhat.com>
|
||
|
|
Date: Thu, 22 Jan 2015 15:51:08 -0800
|
||
|
|
Subject: [PATCH] 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>
|
||
|
|
---
|
||
|
|
|
||
|
|
--- a/net/ipv4/fib_trie.c
|
||
|
|
+++ b/net/ipv4/fib_trie.c
|
||
|
|
@@ -961,12 +961,12 @@ static struct tnode *fib_find_node(struc
|
||
|
|
* 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 *t
|
||
|
|
* 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 */
|