git: 02d0c43c9e53 - main - rb_tree: speed-up double rotation
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Date: Fri, 19 Aug 2022 23:14:08 UTC
The branch main has been updated by dougm:
URL: https://cgit.FreeBSD.org/src/commit/?id=02d0c43c9e53b3055b17719a184a813032040f79
commit 02d0c43c9e53b3055b17719a184a813032040f79
Author: Doug Moore <dougm@FreeBSD.org>
AuthorDate: 2022-08-19 23:11:29 +0000
Commit: Doug Moore <dougm@FreeBSD.org>
CommitDate: 2022-08-19 23:11:29 +0000
rb_tree: speed-up double rotation
RB_ROTATE_LEFT (and it symmetric twin) modify the rb-tree, adjusting
pointers so that what started as a proper tree ends up a proper
tree. When two consecutive rotations move the same node up the tree,
some of the pointers changed in the first rotation are immediately
changed again in the second - namely, the pointer from the rising node
to its new parent, and the pointer from that parent back to the rising
node. This change removes from RB_ROTATE macros the responsibility for
managing those two pointers, and leaves it to the code that calls for
rotations to fix up those pointers afterward. That drops a comparison
and a pair of assignments from every INSERT_COLOR or REMOVE_COLOR call
that ends in a double rotation.
A side-effect of this change is that the SWAP_CHILD macro must take as
a parameter a pointer to the node that is changing children, where it
is now computed from the old child. Since this macro is called in a
couple of places besides the RB_ROTATE macros, those calls are also
affected.
Reviewed by: alc
MFC after: 3 weeks
Differential Revision: https://reviews.freebsd.org/D36266
---
sys/compat/linuxkpi/common/include/linux/rbtree.h | 3 +-
sys/sys/tree.h | 63 ++++++++++++++---------
2 files changed, 41 insertions(+), 25 deletions(-)
diff --git a/sys/compat/linuxkpi/common/include/linux/rbtree.h b/sys/compat/linuxkpi/common/include/linux/rbtree.h
index de5ef0d6a3ce..1db9b1d4fa21 100644
--- a/sys/compat/linuxkpi/common/include/linux/rbtree.h
+++ b/sys/compat/linuxkpi/common/include/linux/rbtree.h
@@ -132,7 +132,8 @@ rb_replace_node(struct rb_node *victim, struct rb_node *new,
struct rb_root *root)
{
- RB_SWAP_CHILD((struct linux_root *)root, victim, new, __entry);
+ RB_SWAP_CHILD((struct linux_root *)root, rb_parent(victim),
+ victim, new, __entry);
if (victim->rb_left)
RB_SET_PARENT(victim->rb_left, new, __entry);
if (victim->rb_right)
diff --git a/sys/sys/tree.h b/sys/sys/tree.h
index d82c341049c6..1d4271c2144a 100644
--- a/sys/sys/tree.h
+++ b/sys/sys/tree.h
@@ -378,31 +378,40 @@ struct { \
} while ((rb_update_tmp = RB_PARENT(rb_update_tmp, field)) != NULL); \
} while (0)
-#define RB_SWAP_CHILD(head, out, in, field) do { \
- if (RB_PARENT(out, field) == NULL) \
+#define RB_SWAP_CHILD(head, par, out, in, field) do { \
+ if (par == NULL) \
RB_ROOT(head) = (in); \
- else if ((out) == RB_LEFT(RB_PARENT(out, field), field)) \
- RB_LEFT(RB_PARENT(out, field), field) = (in); \
+ else if ((out) == RB_LEFT(par, field)) \
+ RB_LEFT(par, field) = (in); \
else \
- RB_RIGHT(RB_PARENT(out, field), field) = (in); \
+ RB_RIGHT(par, field) = (in); \
} while (/*CONSTCOND*/ 0)
-#define RB_ROTATE_LEFT(head, elm, tmp, field) do { \
+/*
+ * RB_ROTATE macros partially restructure the tree to improve
+ * balance. The ROTATE_RIGHT case is just a reflection of the
+ * ROTATE_LEFT case. Initially, tmp is a right child of elm. After
+ * rotation, elm is a left child of tmp, and the subtree that
+ * represented the items between them, which formerly hung to the left
+ * of tmp now hangs to the right of elm. The parent-child
+ * relationship between elm and its former parent is not changed;
+ * where this macro once updated those fields, that is now left to the
+ * caller of RB_ROTATE to clean up, so that a pair of rotations does
+ * not twice update the came pair of pointer fields with distinct
+ * values.
+ */
+#define RB_ROTATE_LEFT(elm, tmp, field) do { \
if ((RB_RIGHT(elm, field) = RB_LEFT(tmp, field)) != NULL) { \
RB_SET_PARENT(RB_RIGHT(elm, field), elm, field); \
} \
- RB_SET_PARENT(tmp, RB_PARENT(elm, field), field); \
- RB_SWAP_CHILD(head, elm, tmp, field); \
RB_LEFT(tmp, field) = (elm); \
RB_SET_PARENT(elm, tmp, field); \
} while (/*CONSTCOND*/ 0)
-#define RB_ROTATE_RIGHT(head, elm, tmp, field) do { \
+#define RB_ROTATE_RIGHT(elm, tmp, field) do { \
if ((RB_LEFT(elm, field) = RB_RIGHT(tmp, field)) != NULL) { \
RB_SET_PARENT(RB_LEFT(elm, field), elm, field); \
} \
- RB_SET_PARENT(tmp, RB_PARENT(elm, field), field); \
- RB_SWAP_CHILD(head, elm, tmp, field); \
RB_RIGHT(tmp, field) = (elm); \
RB_SET_PARENT(elm, tmp, field); \
} while (/*CONSTCOND*/ 0)
@@ -479,8 +488,9 @@ name##_RB_INSERT_COLOR(struct name *head, struct type *elm) \
* when a value has been assigned to 'child' in the previous \
* one. \
*/ \
- struct type *child, *parent; \
+ struct type *child, *gpar, *parent; \
while ((parent = RB_PARENT(elm, field)) != NULL) { \
+ gpar = RB_PARENT(parent, field); \
if (RB_LEFT(parent, field) == elm) { \
if (RB_RED_LEFT(parent, field)) { \
RB_FLIP_LEFT(parent, field); \
@@ -496,7 +506,7 @@ name##_RB_INSERT_COLOR(struct name *head, struct type *elm) \
child = elm; \
else { \
/* coverity[uninit_use] */ \
- RB_ROTATE_LEFT(head, elm, child, field);\
+ RB_ROTATE_LEFT(elm, child, field); \
if (RB_RED_RIGHT(child, field)) \
RB_FLIP_LEFT(parent, field); \
if (RB_RED_LEFT(child, field)) \
@@ -507,7 +517,7 @@ name##_RB_INSERT_COLOR(struct name *head, struct type *elm) \
RB_RED_MASK) == 0) \
elm = child; \
} \
- RB_ROTATE_RIGHT(head, parent, child, field); \
+ RB_ROTATE_RIGHT(parent, child, field); \
} else { \
if (RB_RED_RIGHT(parent, field)) { \
RB_FLIP_RIGHT(parent, field); \
@@ -523,7 +533,7 @@ name##_RB_INSERT_COLOR(struct name *head, struct type *elm) \
child = elm; \
else { \
/* coverity[uninit_use] */ \
- RB_ROTATE_RIGHT(head, elm, child, field);\
+ RB_ROTATE_RIGHT(elm, child, field); \
if (RB_RED_LEFT(child, field)) \
RB_FLIP_RIGHT(parent, field); \
if (RB_RED_RIGHT(child, field)) \
@@ -534,8 +544,10 @@ name##_RB_INSERT_COLOR(struct name *head, struct type *elm) \
RB_RED_MASK) == 0) \
elm = child; \
} \
- RB_ROTATE_LEFT(head, parent, child, field); \
+ RB_ROTATE_LEFT(parent, child, field); \
} \
+ RB_SET_PARENT(child, gpar, field); \
+ RB_SWAP_CHILD(head, gpar, parent, child, field); \
RB_BITS(child, field) &= ~RB_RED_MASK; \
if (elm != child) \
RB_AUGMENT(elm); \
@@ -560,7 +572,7 @@ attr void \
name##_RB_REMOVE_COLOR(struct name *head, \
struct type *parent, struct type *elm) \
{ \
- struct type *sib; \
+ struct type *gpar, *sib; \
if (RB_LEFT(parent, field) == elm && \
RB_RIGHT(parent, field) == elm) { \
RB_BITS(parent, field) &= ~RB_RED_MASK; \
@@ -570,6 +582,7 @@ name##_RB_REMOVE_COLOR(struct name *head, \
return; \
} \
do { \
+ gpar = RB_PARENT(parent, field); \
if (RB_LEFT(parent, field) == elm) { \
if (!RB_RED_LEFT(parent, field)) { \
RB_FLIP_LEFT(parent, field); \
@@ -588,7 +601,7 @@ name##_RB_REMOVE_COLOR(struct name *head, \
continue; \
case RB_RED_R: \
elm = RB_LEFT(sib, field); \
- RB_ROTATE_RIGHT(head, sib, elm, field); \
+ RB_ROTATE_RIGHT(sib, elm, field); \
if (RB_RED_LEFT(elm, field)) \
RB_FLIP_ALL(parent, field); \
else \
@@ -613,7 +626,7 @@ name##_RB_REMOVE_COLOR(struct name *head, \
elm = sib; \
break; \
} \
- RB_ROTATE_LEFT(head, parent, elm, field); \
+ RB_ROTATE_LEFT(parent, elm, field); \
} else { \
if (!RB_RED_RIGHT(parent, field)) { \
RB_FLIP_RIGHT(parent, field); \
@@ -632,7 +645,7 @@ name##_RB_REMOVE_COLOR(struct name *head, \
continue; \
case RB_RED_L: \
elm = RB_RIGHT(sib, field); \
- RB_ROTATE_LEFT(head, sib, elm, field); \
+ RB_ROTATE_LEFT(sib, elm, field); \
if (RB_RED_RIGHT(elm, field)) \
RB_FLIP_ALL(parent, field); \
else \
@@ -657,8 +670,10 @@ name##_RB_REMOVE_COLOR(struct name *head, \
elm = sib; \
break; \
} \
- RB_ROTATE_RIGHT(head, parent, elm, field); \
+ RB_ROTATE_RIGHT(parent, elm, field); \
} \
+ RB_SET_PARENT(elm, gpar, field); \
+ RB_SWAP_CHILD(head, gpar, parent, elm, field); \
if (sib != elm) \
RB_AUGMENT(sib); \
break; \
@@ -669,10 +684,10 @@ name##_RB_REMOVE_COLOR(struct name *head, \
attr struct type * \
name##_RB_REMOVE(struct name *head, struct type *elm) \
{ \
- struct type *child, *old, *parent, *right; \
+ struct type *child, *gpar, *old, *parent, *right; \
\
old = elm; \
- parent = RB_PARENT(elm, field); \
+ gpar = parent = RB_PARENT(elm, field); \
right = RB_RIGHT(elm, field); \
if (RB_LEFT(elm, field) == NULL) \
elm = child = right; \
@@ -695,7 +710,7 @@ name##_RB_REMOVE(struct name *head, struct type *elm) \
RB_SET_PARENT(RB_LEFT(old, field), elm, field); \
elm->field = old->field; \
} \
- RB_SWAP_CHILD(head, old, elm, field); \
+ RB_SWAP_CHILD(head, gpar, old, elm, field); \
if (child != NULL) \
RB_SET_PARENT(child, parent, field); \
if (parent != NULL) { \