[v6,11/16,RESEND] rbtree: optimize fetching of sibling node

Commit Message

Praveen Kumar Nov. 21, 2017, 3:20 p.m. UTC

From: Michel Lespinasse <[e-mail]>

When looking to fetch a node's sibling, we went through a sequence of:
- check if node is the parent's left child
- if it is, then fetch the parent's right child

This can be replaced with:
- fetch the parent's right child as an assumed sibling
- check that node is NOT the fetched child

This avoids fetching the parent's left child when node is actually
that child. Saves a bit on code size, though it doesn't seem to make
a large difference in speed.

Signed-off-by: Michel Lespinasse <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Cc: David Woodhouse <[e-mail]>
Acked-by: Rik van Riel <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Daniel Santos <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Cc: "Eric W. Biederman" <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>
[Linux commit 59633abf34e2f44b8e772a2c12a92132aa7c2220]

Ported to Xen.

Signed-off-by: Praveen Kumar <[e-mail]>
---
 xen/common/rbtree.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

Patch

diff --git a/xen/common/rbtree.c b/xen/common/rbtree.c
index b964171bee..07b0875227 100644
--- a/xen/common/rbtree.c
+++ b/xen/common/rbtree.c
@@ -107,8 +107,8 @@  void rb_insert_color(struct rb_node *node, struct rb_root *root)
 
 		gparent = rb_red_parent(parent);
 
-		if (parent == gparent->rb_left) {
-			tmp = gparent->rb_right;
+		tmp = gparent->rb_right;
+		if (parent != tmp) {    /* parent == gparent->rb_left */
 			if (tmp && rb_is_red(tmp)) {
 				/*
 				 * Case 1 - color flips
@@ -131,7 +131,8 @@  void rb_insert_color(struct rb_node *node, struct rb_root *root)
 				continue;
 			}
 
-			if (parent->rb_right == node) {
+			tmp = parent->rb_right;
+			if (node == tmp) {
 				/*
 				 * Case 2 - left rotate at parent
 				 *
@@ -151,6 +152,7 @@  void rb_insert_color(struct rb_node *node, struct rb_root *root)
 							    RB_BLACK);
 				rb_set_parent_color(parent, node, RB_RED);
 				parent = node;
+				tmp = node->rb_right;
 			}
 
 			/*
@@ -162,7 +164,7 @@  void rb_insert_color(struct rb_node *node, struct rb_root *root)
 			 *     /                 \
 			 *    n                   U
 			 */
-			gparent->rb_left = tmp = parent->rb_right;
+			gparent->rb_left = tmp;  /* == parent->rb_right */
 			parent->rb_right = gparent;
 			if (tmp)
 				rb_set_parent_color(tmp, gparent, RB_BLACK);
@@ -180,7 +182,8 @@  void rb_insert_color(struct rb_node *node, struct rb_root *root)
 				continue;
 			}
 
-			if (parent->rb_left == node) {
+			tmp = parent->rb_left;
+			if (node == tmp) {
 				/* Case 2 - right rotate at parent */
 				parent->rb_left = tmp = node->rb_right;
 				node->rb_right = parent;
@@ -189,10 +192,11 @@  void rb_insert_color(struct rb_node *node, struct rb_root *root)
 							    RB_BLACK);
 				rb_set_parent_color(parent, node, RB_RED);
 				parent = node;
+				tmp = node->rb_left;
 			}
 
 			/* Case 3 - left rotate at gparent */
-			gparent->rb_right = tmp = parent->rb_left;
+			gparent->rb_right = tmp;  /* == parent->rb_left */
 			parent->rb_left = gparent;
 			if (tmp)
 				rb_set_parent_color(tmp, gparent, RB_BLACK);
@@ -223,8 +227,9 @@  static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
 			break;
 		} else if (!parent) {
 			break;
-		} else if (parent->rb_left == node) {
-			sibling = parent->rb_right;
+		}
+		sibling = parent->rb_right;
+		if (node != sibling) {  /* node == parent->rb_left */
 			if (rb_is_red(sibling)) {
 				/*
 				 * Case 1 - left rotate at parent