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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: Michel Lespinasse <walken@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Woodhouse <David.Woodhouse@intel.com>
Acked-by: Rik 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michel Lespinasse 2012-10-08 16:31:02 -07:00 committed by Linus Torvalds
parent 7ce6ff9e5d
commit 59633abf34
1 changed files with 13 additions and 8 deletions
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21
lib/rbtree.c
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@ -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