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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [Resend][PATCH 11/17] rbtree: low level optimizations in __rb_erase_color()
In __rb_erase_color(), we often already have pointers to the nodes being
rotated and/or know what their colors must be, so we can generate more
efficient code than the generic __rb_rotate_left() and __rb_rotate_right()
functions.
Also when the current node is red or when flipping the sibling's color,
the parent is already known so we can use the more efficient
rb_set_parent_color() function to set the desired color.
commit 6280d2356fd8ad0936a63c10dc1e6accf48d0c61 from linux tree
Signed-off-by: Praveen Kumar <kpraveen.lkml@xxxxxxxxx>
---
xen/common/rbtree.c | 197 ++++++++++++++++++++++++++++------------------------
1 file changed, 107 insertions(+), 90 deletions(-)
diff --git a/xen/common/rbtree.c b/xen/common/rbtree.c
index 1e4cb1ed2c..253861d889 100644
--- a/xen/common/rbtree.c
+++ b/xen/common/rbtree.c
@@ -38,7 +38,8 @@
* 5), then the longest possible path due to 4 is 2B.
*
* We shall indicate color with case, where black nodes are uppercase and red
- * nodes will be lowercase.
+ * nodes will be lowercase. Unknown color nodes shall be drawn as red within
+ * parentheses and have some accompanying text comment.
*/
#define RB_RED 0
@@ -47,17 +48,11 @@
#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_set_red(r) do { (r)->__rb_parent_color &= ~1; } while (0)
-#define rb_set_black(r) do { (r)->__rb_parent_color |= 1; } while (0)
static inline void rb_set_parent(struct rb_node *rb, struct rb_node *p)
{
rb->__rb_parent_color = rb_color(rb) | (unsigned long)p;
}
-static inline void rb_set_color(struct rb_node *rb, int color)
-{
- rb->__rb_parent_color = (rb->__rb_parent_color & ~1) | color;
-}
static inline void rb_set_parent_color(struct rb_node *rb,
struct rb_node *p, int color)
@@ -70,52 +65,6 @@ static inline struct rb_node *rb_red_parent(struct rb_node
*red)
return (struct rb_node *)red->__rb_parent_color;
}
-static void __rb_rotate_left(struct rb_node *node, struct rb_root *root)
-{
- struct rb_node *right = node->rb_right;
- struct rb_node *parent = rb_parent(node);
-
- if ((node->rb_right = right->rb_left))
- rb_set_parent(right->rb_left, node);
- right->rb_left = node;
-
- rb_set_parent(right, parent);
-
- if (parent)
- {
- if (node == parent->rb_left)
- parent->rb_left = right;
- else
- parent->rb_right = right;
- }
- else
- root->rb_node = right;
- rb_set_parent(node, right);
-}
-
-static void __rb_rotate_right(struct rb_node *node, struct rb_root *root)
-{
- struct rb_node *left = node->rb_left;
- struct rb_node *parent = rb_parent(node);
-
- if ((node->rb_left = left->rb_right))
- rb_set_parent(left->rb_right, node);
- left->rb_right = node;
-
- rb_set_parent(left, parent);
-
- if (parent)
- {
- if (node == parent->rb_right)
- parent->rb_right = left;
- else
- parent->rb_left = left;
- }
- else
- root->rb_node = left;
- rb_set_parent(node, left);
-}
-
/*
* Helper function for rotations:
* - old's parent and color get assigned to new
@@ -260,7 +209,7 @@ EXPORT_SYMBOL(rb_insert_color);
static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
struct rb_root *root)
{
- struct rb_node *other;
+ struct rb_node *sibling, *tmp1, *tmp2;
while (true)
{
@@ -275,68 +224,136 @@ static void __rb_erase_color(struct rb_node *node,
struct rb_node *parent,
*/
if (node && rb_is_red(node))
{
- rb_set_black(node);
+ rb_set_parent_color(node, parent, RB_BLACK);
break;
} else if (!parent) {
break;
} else if (parent->rb_left == node) {
- other = parent->rb_right;
- if (rb_is_red(other))
- {
- rb_set_black(other);
- rb_set_red(parent);
- __rb_rotate_left(parent, root);
- other = parent->rb_right;
+ sibling = parent->rb_right;
+ if (rb_is_red(sibling)) {
+ /*
+ * Case 1 - left rotate at parent
+ *
+ * P S
+ * / \ / \
+ * N s --> p Sr
+ * / \ / \
+ * Sl Sr N Sl
+ */
+ parent->rb_right = tmp1 = sibling->rb_left;
+ sibling->rb_left = parent;
+ rb_set_parent_color(tmp1, parent, RB_BLACK);
+ __rb_rotate_set_parents(parent, sibling, root, RB_RED);
+ sibling = tmp1;
}
- if (!other->rb_right || rb_is_black(other->rb_right))
+ tmp1 = sibling->rb_right;
+ if (!tmp1 || rb_is_black(tmp1))
{
- if (!other->rb_left || rb_is_black(other->rb_left))
+ tmp2 = sibling->rb_left;
+ if (!tmp2 || rb_is_black(tmp2))
{
- rb_set_red(other);
+ /*
+ * Case 2 - sibling color flip
+ * (p could be either color here)
+ *
+ * (p) (p)
+ * / \ / \
+ * N S --> N s
+ * / \ / \
+ * Sl Sr Sl Sr
+ *
+ * This leaves us violating 5), so
+ * recurse at p. If p is red, the
+ * recursion will just flip it to black
+ * and exit. If coming from Case 1,
+ * p is known to be red.
+ */
+ rb_set_parent_color(sibling, parent, RB_RED);
node = parent;
parent = rb_parent(node);
continue;
}
- rb_set_black(other->rb_left);
- rb_set_red(other);
- __rb_rotate_right(other, root);
- other = parent->rb_right;
+ /*
+ * Case 3 - right rotate at sibling
+ * (p could be either color here)
+ *
+ * (p) (p)
+ * / \ / \
+ * N S --> N Sl
+ * / \ \
+ * sl Sr s
+ * \
+ * Sr
+ */
+ sibling->rb_left = tmp1 = tmp2->rb_right;
+ tmp2->rb_right = sibling;
+ parent->rb_right = tmp2;
+ if (tmp1)
+ rb_set_parent_color(tmp1, sibling, RB_BLACK);
+ tmp1 = sibling;
+ sibling = tmp2;
}
- rb_set_color(other, rb_color(parent));
- rb_set_black(parent);
- rb_set_black(other->rb_right);
- __rb_rotate_left(parent, root);
+ /*
+ * Case 4 - left rotate at parent + color flips
+ * (p and sl could be either color here.
+ * After rotation, p becomes black, s acquires
+ * p's color, and sl keeps its color)
+ *
+ * (p) (s)
+ * / \ / \
+ * N S --> P Sr
+ * / \ / \
+ * (sl) sr N (sl)
+ */
+ parent->rb_right = tmp2 = sibling->rb_left;
+ sibling->rb_left = parent;
+ rb_set_parent_color(tmp1, sibling, RB_BLACK);
+ if (tmp2)
+ rb_set_parent(tmp2, parent);
+ __rb_rotate_set_parents(parent, sibling, root, RB_BLACK);
break;
}
else
{
- other = parent->rb_left;
- if (rb_is_red(other))
+ sibling = parent->rb_left;
+ if (rb_is_red(sibling))
{
- rb_set_black(other);
- rb_set_red(parent);
- __rb_rotate_right(parent, root);
- other = parent->rb_left;
+ /* Case 1 - right rotate at parent */
+ parent->rb_left = tmp1 = sibling->rb_right;
+ sibling->rb_right = parent;
+ rb_set_parent_color(tmp1, parent, RB_BLACK);
+ __rb_rotate_set_parents(parent, sibling, root, RB_RED);
+ sibling = tmp1;
}
- if (!other->rb_left || rb_is_black(other->rb_left))
+ tmp1 = sibling->rb_left;
+ if (!tmp1 || rb_is_black(tmp1))
{
- if (!other->rb_right || rb_is_black(other->rb_right))
+ tmp2 = sibling->rb_right;
+ if (!tmp2 || rb_is_black(tmp2))
{
- rb_set_red(other);
+ /* Case 2 - sibling color flip */
+ rb_set_parent_color(sibling, parent, RB_RED);
node = parent;
parent = rb_parent(node);
continue;
}
- rb_set_black(other->rb_right);
- rb_set_red(other);
- __rb_rotate_left(other, root);
- other = parent->rb_left;
+ /* Case 3 - right rotate at sibling */
+ sibling->rb_right = tmp1 = tmp2->rb_left;
+ tmp2->rb_left = sibling;
+ parent->rb_left = tmp2;
+ if (tmp1)
+ rb_set_parent_color(tmp1, sibling, RB_BLACK);
+ tmp1 = sibling;
+ sibling = tmp2;
}
- rb_set_color(other, rb_color(parent));
- rb_set_black(parent);
- rb_set_black(other->rb_left);
- __rb_rotate_right(parent, root);
+ /* Case 4 - left rotate at parent + color flips */
+ parent->rb_left = tmp2 = sibling->rb_right;
+ sibling->rb_right = parent;
+ rb_set_parent_color(tmp1, sibling, RB_BLACK);
+ if (tmp2)
+ rb_set_parent(tmp2, parent);
+ __rb_rotate_set_parents(parent, sibling, root, RB_BLACK);
break;
}
}
--
2.12.0
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