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fib_trie: Use index & (~0ul << n->bits) instead of index >> n->bits

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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>
This commit is contained in:
Alexander Duyck 2015-01-22 15:51:08 -08:00 committed by David S. Miller
parent bc579ae5f9
commit b3832117b4
1 changed files with 8 additions and 8 deletions
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16
net/ipv4/fib_trie.c
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@ -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 */