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53 lines
1.9 KiB
Diff
53 lines
1.9 KiB
Diff
From: Alexander Duyck <alexander.h.duyck@redhat.com>
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Date: Thu, 22 Jan 2015 15:51:08 -0800
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Subject: [PATCH] fib_trie: Use index & (~0ul << n->bits) instead of index >>
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n->bits
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In doing performance testing and analysis of the changes I recently found
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that by shifting the index I had created an unnecessary dependency.
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I have updated the code so that we instead shift a mask by bits and then
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just test against that as that should save us about 2 CPU cycles since we
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can generate the mask while the key and pos are being processed.
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Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
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Signed-off-by: David S. Miller <davem@davemloft.net>
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---
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--- a/net/ipv4/fib_trie.c
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+++ b/net/ipv4/fib_trie.c
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@@ -961,12 +961,12 @@ static struct tnode *fib_find_node(struc
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* prefix plus zeros for the bits in the cindex. The index
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* is the difference between the key and this value. From
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* this we can actually derive several pieces of data.
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- * if !(index >> bits)
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- * we know the value is cindex
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- * else
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+ * if (index & (~0ul << bits))
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* we have a mismatch in skip bits and failed
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+ * else
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+ * we know the value is cindex
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*/
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- if (index >> n->bits)
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+ if (index & (~0ul << n->bits))
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return NULL;
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/* we have found a leaf. Prefixes have already been compared */
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@@ -1301,12 +1301,12 @@ int fib_table_lookup(struct fib_table *t
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* prefix plus zeros for the "bits" in the prefix. The index
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* is the difference between the key and this value. From
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* this we can actually derive several pieces of data.
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- * if !(index >> bits)
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- * we know the value is child index
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- * else
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+ * if (index & (~0ul << bits))
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* we have a mismatch in skip bits and failed
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+ * else
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+ * we know the value is cindex
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*/
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- if (index >> n->bits)
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+ if (index & (~0ul << n->bits))
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break;
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/* we have found a leaf. Prefixes have already been compared */
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