Commit 59633abf authored by Michel Lespinasse's avatar Michel Lespinasse Committed by Linus Torvalds
Browse files

rbtree: optimize fetching of sibling node 



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: default avatarMichel Lespinasse <walken@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Woodhouse <David.Woodhouse@intel.com>
Acked-by: default avatarRik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Daniel Santos <daniel.santos@pobox.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7ce6ff9e

lib/rbtree.c

+13 −8
Original line number Diff line number Diff line
@@ -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;

		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;

		if (node != sibling) {	/* node == parent->rb_left */

			if (rb_is_red(sibling)) {

				/*

				 * Case 1 - left rotate at parent

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