target/linux/generic/patches-3.18/080-17-fib_trie-Remove-checks-for-index-tnode_child_length-.patch

   1 From: Alexander Duyck <alexander.h.duyck@redhat.com>
   2 Date: Wed, 31 Dec 2014 10:57:02 -0800
   3 Subject: [PATCH] fib_trie: Remove checks for index >= tnode_child_length
   4  from tnode_get_child
   5
   6 For some reason the compiler doesn't seem to understand that when we are in
   7 a loop that runs from tnode_child_length - 1 to 0 we don't expect the value
   8 of tn->bits to change.  As such every call to tnode_get_child was rerunning
   9 tnode_chile_length which ended up consuming quite a bit of space in the
  10 resultant assembly code.
  11
  12 I have gone though and verified that in all cases where tnode_get_child
  13 is used we are either winding though a fixed loop from tnode_child_length -
  14 1 to 0, or are in a fastpath case where we are verifying the value by
  15 either checking for any remaining bits after shifting index by bits and
  16 testing for leaf, or by using tnode_child_length.
  17
  18 size net/ipv4/fib_trie.o
  19 Before:
  20    text    data     bss     dec     hex filename
  21   15506     376       8   15890    3e12 net/ipv4/fib_trie.o
  22
  23 After:
  24    text    data     bss     dec     hex filename
  25   14827     376       8   15211    3b6b net/ipv4/fib_trie.o
  26
  27 Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
  28 Signed-off-by: David S. Miller <davem@davemloft.net>
  29 ---
  30
  31 --- a/net/ipv4/fib_trie.c
  32 +++ b/net/ipv4/fib_trie.c
  33 @@ -186,8 +186,6 @@ static inline unsigned long tnode_child_
  34  static inline struct tnode *tnode_get_child(const struct tnode *tn,
  35                                             unsigned long i)
  36  {
  37 -       BUG_ON(i >= tnode_child_length(tn));
  38 -
  39         return rtnl_dereference(tn->child[i]);
  40  }
  41
  42 @@ -195,8 +193,6 @@ static inline struct tnode *tnode_get_ch
  43  static inline struct tnode *tnode_get_child_rcu(const struct tnode *tn,
  44                                                 unsigned long i)
  45  {
  46 -       BUG_ON(i >= tnode_child_length(tn));
  47 -
  48         return rcu_dereference_rtnl(tn->child[i]);
  49  }
  50
  51 @@ -371,7 +367,7 @@ static inline int tnode_full(const struc
  52   */
  53  static void put_child(struct tnode *tn, unsigned long i, struct tnode *n)
  54  {
  55 -       struct tnode *chi = rtnl_dereference(tn->child[i]);
  56 +       struct tnode *chi = tnode_get_child(tn, i);
  57         int isfull, wasfull;
  58
  59         BUG_ON(i >= tnode_child_length(tn));
  60 @@ -867,7 +863,7 @@ static struct tnode *fib_find_node(struc
  61                 if (IS_LEAF(n))
  62                         break;
  63
  64 -               n = rcu_dereference_rtnl(n->child[index]);
  65 +               n = tnode_get_child_rcu(n, index);
  66         }
  67
  68         return n;
  69 @@ -934,7 +930,7 @@ static struct list_head *fib_insert_node
  70                 }
  71
  72                 tp = n;
  73 -               n = rcu_dereference_rtnl(n->child[index]);
  74 +               n = tnode_get_child_rcu(n, index);
  75         }
  76
  77         l = leaf_new(key);
  78 @@ -1215,7 +1211,7 @@ int fib_table_lookup(struct fib_table *t
  79                         cindex = index;
  80                 }
  81
  82 -               n = rcu_dereference(n->child[index]);
  83 +               n = tnode_get_child_rcu(n, index);
  84                 if (unlikely(!n))
  85                         goto backtrace;
  86         }
  87 @@ -1835,7 +1831,7 @@ static void trie_collect_stats(struct tr
  88                         if (n->bits < MAX_STAT_DEPTH)
  89                                 s->nodesizes[n->bits]++;
  90
  91 -                       for (i = 0; i < tnode_child_length(n); i++) {
  92 +                       for (i = tnode_child_length(n); i--;) {
  93                                 if (!rcu_access_pointer(n->child[i]))
  94                                         s->nullpointers++;
  95                         }