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authorMichel Lespinasse <walken@google.com>2012-10-08 16:31:13 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-10-09 16:22:37 +0900
commit4f035ad67f4633c233cb3642711d49b4efc9c82d (patch)
tree151fd5ff00a07da479805a01cb8b1d370db72d8f /lib
parent46b6135a7402ac23c5b25f2bd79b03bab8f98278 (diff)
downloadvexpress-lsk-4f035ad67f4633c233cb3642711d49b4efc9c82d.tar.gz
rbtree: low level optimizations in rb_erase()
Various minor optimizations in rb_erase(): - Avoid multiple loading of node->__rb_parent_color when computing parent and color information (possibly not in close sequence, as there might be further branches in the algorithm) - In the 1-child subcase of case 1, copy the __rb_parent_color field from the erased node to the child instead of recomputing it from the desired parent and color - When searching for the erased node's successor, differentiate between cases 2 and 3 based on whether any left links were followed. This avoids a condition later down. - In case 3, keep a pointer to the erased node's right child so we don't have to refetch it later to adjust its parent. - In the no-childs subcase of cases 2 and 3, place the rebalance assigment last so that the compiler can remove the following if(rebalance) test. Also, added some comments to illustrate cases 2 and 3. Signed-off-by: Michel Lespinasse <walken@google.com> Acked-by: Rik van Riel <riel@redhat.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: David Woodhouse <dwmw2@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib')
-rw-r--r--lib/rbtree.c98
1 files changed, 64 insertions, 34 deletions
diff --git a/lib/rbtree.c b/lib/rbtree.c
index 80b092538fa..938061ecbe6 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -47,9 +47,14 @@
#define RB_RED 0
#define RB_BLACK 1
-#define rb_color(r) ((r)->__rb_parent_color & 1)
-#define rb_is_red(r) (!rb_color(r))
-#define rb_is_black(r) rb_color(r)
+#define __rb_parent(pc) ((struct rb_node *)(pc & ~3))
+
+#define __rb_color(pc) ((pc) & 1)
+#define __rb_is_black(pc) __rb_color(pc)
+#define __rb_is_red(pc) (!__rb_color(pc))
+#define rb_color(rb) __rb_color((rb)->__rb_parent_color)
+#define rb_is_red(rb) __rb_is_red((rb)->__rb_parent_color)
+#define rb_is_black(rb) __rb_is_black((rb)->__rb_parent_color)
static inline void rb_set_black(struct rb_node *rb)
{
@@ -378,6 +383,7 @@ void rb_erase(struct rb_node *node, struct rb_root *root)
{
struct rb_node *child = node->rb_right, *tmp = node->rb_left;
struct rb_node *parent, *rebalance;
+ unsigned long pc;
if (!tmp) {
/*
@@ -387,51 +393,75 @@ void rb_erase(struct rb_node *node, struct rb_root *root)
* and node must be black due to 4). We adjust colors locally
* so as to bypass __rb_erase_color() later on.
*/
-
- parent = rb_parent(node);
+ pc = node->__rb_parent_color;
+ parent = __rb_parent(pc);
__rb_change_child(node, child, parent, root);
if (child) {
- rb_set_parent_color(child, parent, RB_BLACK);
+ child->__rb_parent_color = pc;
rebalance = NULL;
- } else {
- rebalance = rb_is_black(node) ? parent : NULL;
- }
+ } else
+ rebalance = __rb_is_black(pc) ? parent : NULL;
} else if (!child) {
/* Still case 1, but this time the child is node->rb_left */
- parent = rb_parent(node);
+ tmp->__rb_parent_color = pc = node->__rb_parent_color;
+ parent = __rb_parent(pc);
__rb_change_child(node, tmp, parent, root);
- rb_set_parent_color(tmp, parent, RB_BLACK);
rebalance = NULL;
} else {
- struct rb_node *old = node, *left;
-
- node = child;
- while ((left = node->rb_left) != NULL)
- node = left;
-
- __rb_change_child(old, node, rb_parent(old), root);
-
- child = node->rb_right;
- parent = rb_parent(node);
-
- if (parent == old) {
- parent = node;
+ struct rb_node *successor = child, *child2;
+ tmp = child->rb_left;
+ if (!tmp) {
+ /*
+ * Case 2: node's successor is its right child
+ *
+ * (n) (s)
+ * / \ / \
+ * (x) (s) -> (x) (c)
+ * \
+ * (c)
+ */
+ parent = child;
+ child2 = child->rb_right;
} else {
- parent->rb_left = child;
-
- node->rb_right = old->rb_right;
- rb_set_parent(old->rb_right, node);
+ /*
+ * Case 3: node's successor is leftmost under
+ * node's right child subtree
+ *
+ * (n) (s)
+ * / \ / \
+ * (x) (y) -> (x) (y)
+ * / /
+ * (p) (p)
+ * / /
+ * (s) (c)
+ * \
+ * (c)
+ */
+ do {
+ parent = successor;
+ successor = tmp;
+ tmp = tmp->rb_left;
+ } while (tmp);
+ parent->rb_left = child2 = successor->rb_right;
+ successor->rb_right = child;
+ rb_set_parent(child, successor);
}
- if (child) {
- rb_set_parent_color(child, parent, RB_BLACK);
+ successor->rb_left = tmp = node->rb_left;
+ rb_set_parent(tmp, successor);
+
+ pc = node->__rb_parent_color;
+ tmp = __rb_parent(pc);
+ __rb_change_child(node, successor, tmp, root);
+ if (child2) {
+ successor->__rb_parent_color = pc;
+ rb_set_parent_color(child2, parent, RB_BLACK);
rebalance = NULL;
} else {
- rebalance = rb_is_black(node) ? parent : NULL;
+ unsigned long pc2 = successor->__rb_parent_color;
+ successor->__rb_parent_color = pc;
+ rebalance = __rb_is_black(pc2) ? parent : NULL;
}
- node->__rb_parent_color = old->__rb_parent_color;
- node->rb_left = old->rb_left;
- rb_set_parent(old->rb_left, node);
}
if (rebalance)