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347 lines
12 KiB
347 lines
12 KiB
![]()
10 years ago
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From: Alexander Duyck <alexander.h.duyck@redhat.com>
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Date: Wed, 31 Dec 2014 10:56:12 -0800
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Subject: [PATCH] fib_trie: Update meaning of pos to represent unchecked
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bits
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This change moves the pos value to the other side of the "bits" field. By
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doing this it actually simplifies a significant amount of code in the trie.
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For example when halving a tree we know that the bit lost exists at
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oldnode->pos, and if we inflate the tree the new bit being add is at
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tn->pos. Previously to find those bits you would have to subtract pos and
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bits from the keylength or start with a value of (1 << 31) and then shift
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that.
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There are a number of spots throughout the code that benefit from this. In
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the case of the hot-path searches the main advantage is that we can drop 2
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or more operations from the search path as we no longer need to compute the
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value for the index to be shifted by and can instead just use the raw pos
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value.
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In addition the tkey_extract_bits is now defunct and can be replaced by
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get_index since the two operations were doing the same thing, but now
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get_index does it much more quickly as it is only an xor and shift versus a
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pair of shifts and a subtraction.
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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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@@ -90,8 +90,7 @@ typedef unsigned int t_key;
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#define IS_TNODE(n) ((n)->bits)
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#define IS_LEAF(n) (!(n)->bits)
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-#define get_shift(_kv) (KEYLENGTH - (_kv)->pos - (_kv)->bits)
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-#define get_index(_key, _kv) (((_key) ^ (_kv)->key) >> get_shift(_kv))
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+#define get_index(_key, _kv) (((_key) ^ (_kv)->key) >> (_kv)->pos)
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struct tnode {
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t_key key;
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@@ -209,81 +208,64 @@ static inline struct tnode *tnode_get_ch
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return rcu_dereference_rtnl(tn->child[i]);
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}
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-static inline t_key mask_pfx(t_key k, unsigned int l)
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-{
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- return (l == 0) ? 0 : k >> (KEYLENGTH-l) << (KEYLENGTH-l);
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-}
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-
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-static inline t_key tkey_extract_bits(t_key a, unsigned int offset, unsigned int bits)
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-{
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- if (offset < KEYLENGTH)
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- return ((t_key)(a << offset)) >> (KEYLENGTH - bits);
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- else
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- return 0;
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-}
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-
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-/*
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- To understand this stuff, an understanding of keys and all their bits is
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- necessary. Every node in the trie has a key associated with it, but not
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- all of the bits in that key are significant.
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-
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- Consider a node 'n' and its parent 'tp'.
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-
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- If n is a leaf, every bit in its key is significant. Its presence is
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- necessitated by path compression, since during a tree traversal (when
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- searching for a leaf - unless we are doing an insertion) we will completely
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- ignore all skipped bits we encounter. Thus we need to verify, at the end of
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- a potentially successful search, that we have indeed been walking the
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- correct key path.
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-
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- Note that we can never "miss" the correct key in the tree if present by
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- following the wrong path. Path compression ensures that segments of the key
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- that are the same for all keys with a given prefix are skipped, but the
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- skipped part *is* identical for each node in the subtrie below the skipped
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- bit! trie_insert() in this implementation takes care of that - note the
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- call to tkey_sub_equals() in trie_insert().
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-
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- if n is an internal node - a 'tnode' here, the various parts of its key
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- have many different meanings.
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-
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- Example:
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- _________________________________________________________________
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- | i | i | i | i | i | i | i | N | N | N | S | S | S | S | S | C |
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- -----------------------------------------------------------------
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- 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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-
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- _________________________________________________________________
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- | C | C | C | u | u | u | u | u | u | u | u | u | u | u | u | u |
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- -----------------------------------------------------------------
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- 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
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-
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- tp->pos = 7
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- tp->bits = 3
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- n->pos = 15
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- n->bits = 4
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-
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- First, let's just ignore the bits that come before the parent tp, that is
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- the bits from 0 to (tp->pos-1). They are *known* but at this point we do
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- not use them for anything.
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-
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- The bits from (tp->pos) to (tp->pos + tp->bits - 1) - "N", above - are the
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- index into the parent's child array. That is, they will be used to find
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- 'n' among tp's children.
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-
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- The bits from (tp->pos + tp->bits) to (n->pos - 1) - "S" - are skipped bits
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- for the node n.
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-
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- All the bits we have seen so far are significant to the node n. The rest
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- of the bits are really not needed or indeed known in n->key.
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-
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- The bits from (n->pos) to (n->pos + n->bits - 1) - "C" - are the index into
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- n's child array, and will of course be different for each child.
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-
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-
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- The rest of the bits, from (n->pos + n->bits) onward, are completely unknown
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- at this point.
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-
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-*/
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+/* To understand this stuff, an understanding of keys and all their bits is
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+ * necessary. Every node in the trie has a key associated with it, but not
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+ * all of the bits in that key are significant.
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+ *
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+ * Consider a node 'n' and its parent 'tp'.
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+ *
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+ * If n is a leaf, every bit in its key is significant. Its presence is
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+ * necessitated by path compression, since during a tree traversal (when
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+ * searching for a leaf - unless we are doing an insertion) we will completely
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+ * ignore all skipped bits we encounter. Thus we need to verify, at the end of
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+ * a potentially successful search, that we have indeed been walking the
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+ * correct key path.
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+ *
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+ * Note that we can never "miss" the correct key in the tree if present by
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+ * following the wrong path. Path compression ensures that segments of the key
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+ * that are the same for all keys with a given prefix are skipped, but the
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+ * skipped part *is* identical for each node in the subtrie below the skipped
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+ * bit! trie_insert() in this implementation takes care of that.
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+ *
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+ * if n is an internal node - a 'tnode' here, the various parts of its key
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+ * have many different meanings.
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+ *
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+ * Example:
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+ * _________________________________________________________________
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+ * | i | i | i | i | i | i | i | N | N | N | S | S | S | S | S | C |
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+ * -----------------------------------------------------------------
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+ * 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
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+ *
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+ * _________________________________________________________________
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+ * | C | C | C | u | u | u | u | u | u | u | u | u | u | u | u | u |
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+ * -----------------------------------------------------------------
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+ * 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
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+ *
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+ * tp->pos = 22
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+ * tp->bits = 3
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+ * n->pos = 13
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+ * n->bits = 4
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+ *
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+ * First, let's just ignore the bits that come before the parent tp, that is
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+ * the bits from (tp->pos + tp->bits) to 31. They are *known* but at this
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+ * point we do not use them for anything.
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+ *
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+ * The bits from (tp->pos) to (tp->pos + tp->bits - 1) - "N", above - are the
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+ * index into the parent's child array. That is, they will be used to find
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+ * 'n' among tp's children.
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+ *
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+ * The bits from (n->pos + n->bits) to (tn->pos - 1) - "S" - are skipped bits
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+ * for the node n.
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+ *
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+ * All the bits we have seen so far are significant to the node n. The rest
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+ * of the bits are really not needed or indeed known in n->key.
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+ *
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+ * The bits from (n->pos) to (n->pos + n->bits - 1) - "C" - are the index into
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+ * n's child array, and will of course be different for each child.
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+ *
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+ * The rest of the bits, from 0 to (n->pos + n->bits), are completely unknown
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+ * at this point.
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+ */
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static const int halve_threshold = 25;
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static const int inflate_threshold = 50;
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@@ -367,7 +349,7 @@ static struct tnode *leaf_new(t_key key)
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* as the nodes are searched
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*/
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l->key = key;
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- l->pos = KEYLENGTH;
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+ l->pos = 0;
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/* set bits to 0 indicating we are not a tnode */
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l->bits = 0;
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@@ -400,7 +382,7 @@ static struct tnode *tnode_new(t_key key
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tn->parent = NULL;
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tn->pos = pos;
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tn->bits = bits;
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- tn->key = mask_pfx(key, pos);
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+ tn->key = (shift < KEYLENGTH) ? (key >> shift) << shift : 0;
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tn->full_children = 0;
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tn->empty_children = 1<<bits;
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}
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@@ -410,14 +392,12 @@ static struct tnode *tnode_new(t_key key
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return tn;
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}
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-/*
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- * Check whether a tnode 'n' is "full", i.e. it is an internal node
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+/* Check whether a tnode 'n' is "full", i.e. it is an internal node
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* and no bits are skipped. See discussion in dyntree paper p. 6
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*/
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-
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static inline int tnode_full(const struct tnode *tn, const struct tnode *n)
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{
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- return n && IS_TNODE(n) && (n->pos == (tn->pos + tn->bits));
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+ return n && ((n->pos + n->bits) == tn->pos) && IS_TNODE(n);
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}
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static inline void put_child(struct tnode *tn, int i,
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@@ -641,11 +621,12 @@ static struct tnode *inflate(struct trie
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{
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int olen = tnode_child_length(oldtnode);
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struct tnode *tn;
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+ t_key m;
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int i;
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pr_debug("In inflate\n");
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- tn = tnode_new(oldtnode->key, oldtnode->pos, oldtnode->bits + 1);
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+ tn = tnode_new(oldtnode->key, oldtnode->pos - 1, oldtnode->bits + 1);
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if (!tn)
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return ERR_PTR(-ENOMEM);
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@@ -656,21 +637,18 @@ static struct tnode *inflate(struct trie
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* fails. In case of failure we return the oldnode and inflate
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* of tnode is ignored.
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*/
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+ for (i = 0, m = 1u << tn->pos; i < olen; i++) {
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+ struct tnode *inode = tnode_get_child(oldtnode, i);
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- for (i = 0; i < olen; i++) {
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- struct tnode *inode;
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-
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- inode = tnode_get_child(oldtnode, i);
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- if (tnode_full(oldtnode, inode) && inode->bits > 1) {
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+ if (tnode_full(oldtnode, inode) && (inode->bits > 1)) {
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struct tnode *left, *right;
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- t_key m = ~0U << (KEYLENGTH - 1) >> inode->pos;
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- left = tnode_new(inode->key&(~m), inode->pos + 1,
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+ left = tnode_new(inode->key & ~m, inode->pos,
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inode->bits - 1);
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if (!left)
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goto nomem;
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- right = tnode_new(inode->key|m, inode->pos + 1,
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+ right = tnode_new(inode->key | m, inode->pos,
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inode->bits - 1);
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if (!right) {
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@@ -694,9 +672,7 @@ static struct tnode *inflate(struct trie
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/* A leaf or an internal node with skipped bits */
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if (!tnode_full(oldtnode, inode)) {
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- put_child(tn,
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- tkey_extract_bits(inode->key, tn->pos, tn->bits),
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- inode);
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+ put_child(tn, get_index(inode->key, tn), inode);
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continue;
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}
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@@ -767,7 +743,7 @@ static struct tnode *halve(struct trie *
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pr_debug("In halve\n");
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- tn = tnode_new(oldtnode->key, oldtnode->pos, oldtnode->bits - 1);
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+ tn = tnode_new(oldtnode->key, oldtnode->pos + 1, oldtnode->bits - 1);
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if (!tn)
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return ERR_PTR(-ENOMEM);
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@@ -787,7 +763,7 @@ static struct tnode *halve(struct trie *
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if (left && right) {
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struct tnode *newn;
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- newn = tnode_new(left->key, tn->pos + tn->bits, 1);
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+ newn = tnode_new(left->key, oldtnode->pos, 1);
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if (!newn)
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goto nomem;
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@@ -915,7 +891,7 @@ static void trie_rebalance(struct trie *
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key = tn->key;
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while (tn != NULL && (tp = node_parent(tn)) != NULL) {
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- cindex = tkey_extract_bits(key, tp->pos, tp->bits);
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+ cindex = get_index(key, tp);
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wasfull = tnode_full(tp, tnode_get_child(tp, cindex));
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tn = resize(t, tn);
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@@ -1005,11 +981,8 @@ static struct list_head *fib_insert_node
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*/
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if (n) {
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struct tnode *tn;
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- int newpos;
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-
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- newpos = KEYLENGTH - __fls(n->key ^ key) - 1;
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- tn = tnode_new(key, newpos, 1);
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+ tn = tnode_new(key, __fls(key ^ n->key), 1);
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if (!tn) {
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free_leaf_info(li);
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node_free(l);
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![]()
10 years ago
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@@ -1559,12 +1532,7 @@ static int trie_flush_leaf(struct tnode
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![]()
10 years ago
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static struct tnode *leaf_walk_rcu(struct tnode *p, struct tnode *c)
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{
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do {
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- t_key idx;
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-
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- if (c)
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- idx = tkey_extract_bits(c->key, p->pos, p->bits) + 1;
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- else
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- idx = 0;
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+ t_key idx = c ? idx = get_index(c->key, p) + 1 : 0;
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while (idx < 1u << p->bits) {
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c = tnode_get_child_rcu(p, idx++);
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@@ -1851,7 +1819,7 @@ rescan:
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/* Current node exhausted, pop back up */
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p = node_parent_rcu(tn);
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if (p) {
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- cindex = tkey_extract_bits(tn->key, p->pos, p->bits)+1;
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+ cindex = get_index(tn->key, p) + 1;
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tn = p;
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--iter->depth;
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goto rescan;
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![]()
10 years ago
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@@ -2186,10 +2154,10 @@ static int fib_trie_seq_show(struct seq_
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![]()
10 years ago
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if (IS_TNODE(n)) {
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__be32 prf = htonl(n->key);
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- seq_indent(seq, iter->depth - 1);
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- seq_printf(seq, " +-- %pI4/%d %d %d %d\n",
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- &prf, n->pos, n->bits, n->full_children,
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- n->empty_children);
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+ seq_indent(seq, iter->depth-1);
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+ seq_printf(seq, " +-- %pI4/%zu %u %u %u\n",
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+ &prf, KEYLENGTH - n->pos - n->bits, n->bits,
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+ n->full_children, n->empty_children);
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} else {
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struct leaf_info *li;
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__be32 val = htonl(n->key);
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