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rbtree: low level optimizations in __rb_erase_color()
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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.

Signed-off-by: Michel Lespinasse <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Acked-by: David Woodhouse <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Daniel Santos <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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@walken-google @torvalds
walken-google authored and torvalds committed Oct 9, 2012
1 parent e125d14 commit 6280d23
Showing 1 changed file with 115 additions and 93 deletions.
208 changes: 115 additions & 93 deletions lib/rbtree.c
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Original file line number Diff line number Diff line change
Expand Up @@ -39,7 +39,8 @@
* 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
Expand All @@ -48,17 +49,11 @@
#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)
Expand All @@ -71,52 +66,6 @@ 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
Expand Down Expand Up @@ -257,7 +206,7 @@ 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) {
/*
Expand All @@ -270,63 +219,136 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
* and tree rotations as per one of the 4 cases below.
*/
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)) {
if (!other->rb_left ||
rb_is_black(other->rb_left)) {
rb_set_red(other);
tmp1 = sibling->rb_right;
if (!tmp1 || rb_is_black(tmp1)) {
tmp2 = sibling->rb_left;
if (!tmp2 || rb_is_black(tmp2)) {
/*
* 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))
{
rb_set_black(other);
rb_set_red(parent);
__rb_rotate_right(parent, root);
other = parent->rb_left;
sibling = parent->rb_left;
if (rb_is_red(sibling)) {
/* 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)) {
if (!other->rb_right ||
rb_is_black(other->rb_right)) {
rb_set_red(other);
tmp1 = sibling->rb_left;
if (!tmp1 || rb_is_black(tmp1)) {
tmp2 = sibling->rb_right;
if (!tmp2 || rb_is_black(tmp2)) {
/* 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;
}
}
Expand Down

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