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Message-Id: <20181206191819.30182-2-dave@stgolabs.net>
Date: Thu, 6 Dec 2018 11:18:13 -0800
From: Davidlohr Bueso <dave@...olabs.net>
To: acme@...nel.org
Cc: mingo@...nel.org, linux-kernel@...r.kernel.org, dave@...olabs.net,
Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 1/7] tools/perf: Update rbtree implementation
There have been a number of changes in the kernel's rbrtee
implementation, including loose lockless searching guarantees
and rb_root_cached, which later patches will use as an
optimization.
Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
tools/include/linux/rbtree.h | 52 ++++++++--
tools/include/linux/rbtree_augmented.h | 60 ++++++++---
tools/lib/rbtree.c | 178 +++++++++++++++++++++++++--------
3 files changed, 229 insertions(+), 61 deletions(-)
diff --git a/tools/include/linux/rbtree.h b/tools/include/linux/rbtree.h
index 112582253dd0..8e9ed4786269 100644
--- a/tools/include/linux/rbtree.h
+++ b/tools/include/linux/rbtree.h
@@ -43,13 +43,28 @@ struct rb_root {
struct rb_node *rb_node;
};
+/*
+ * Leftmost-cached rbtrees.
+ *
+ * We do not cache the rightmost node based on footprint
+ * size vs number of potential users that could benefit
+ * from O(1) rb_last(). Just not worth it, users that want
+ * this feature can always implement the logic explicitly.
+ * Furthermore, users that want to cache both pointers may
+ * find it a bit asymmetric, but that's ok.
+ */
+struct rb_root_cached {
+ struct rb_root rb_root;
+ struct rb_node *rb_leftmost;
+};
#define rb_parent(r) ((struct rb_node *)((r)->__rb_parent_color & ~3))
#define RB_ROOT (struct rb_root) { NULL, }
+#define RB_ROOT_CACHED (struct rb_root_cached) { {NULL, }, NULL }
#define rb_entry(ptr, type, member) container_of(ptr, type, member)
-#define RB_EMPTY_ROOT(root) ((root)->rb_node == NULL)
+#define RB_EMPTY_ROOT(root) (READ_ONCE((root)->rb_node) == NULL)
/* 'empty' nodes are nodes that are known not to be inserted in an rbtree */
#define RB_EMPTY_NODE(node) \
@@ -68,6 +83,12 @@ extern struct rb_node *rb_prev(const struct rb_node *);
extern struct rb_node *rb_first(const struct rb_root *);
extern struct rb_node *rb_last(const struct rb_root *);
+extern void rb_insert_color_cached(struct rb_node *,
+ struct rb_root_cached *, bool);
+extern void rb_erase_cached(struct rb_node *node, struct rb_root_cached *);
+/* Same as rb_first(), but O(1) */
+#define rb_first_cached(root) (root)->rb_leftmost
+
/* Postorder iteration - always visit the parent after its children */
extern struct rb_node *rb_first_postorder(const struct rb_root *);
extern struct rb_node *rb_next_postorder(const struct rb_node *);
@@ -75,6 +96,8 @@ extern struct rb_node *rb_next_postorder(const struct rb_node *);
/* Fast replacement of a single node without remove/rebalance/add/rebalance */
extern void rb_replace_node(struct rb_node *victim, struct rb_node *new,
struct rb_root *root);
+extern void rb_replace_node_cached(struct rb_node *victim, struct rb_node *new,
+ struct rb_root_cached *root);
static inline void rb_link_node(struct rb_node *node, struct rb_node *parent,
struct rb_node **rb_link)
@@ -90,12 +113,29 @@ static inline void rb_link_node(struct rb_node *node, struct rb_node *parent,
____ptr ? rb_entry(____ptr, type, member) : NULL; \
})
-
-/*
- * Handy for checking that we are not deleting an entry that is
- * already in a list, found in block/{blk-throttle,cfq-iosched}.c,
- * probably should be moved to lib/rbtree.c...
+/**
+ * rbtree_postorder_for_each_entry_safe - iterate in post-order over rb_root of
+ * given type allowing the backing memory of @pos to be invalidated
+ *
+ * @pos: the 'type *' to use as a loop cursor.
+ * @n: another 'type *' to use as temporary storage
+ * @root: 'rb_root *' of the rbtree.
+ * @field: the name of the rb_node field within 'type'.
+ *
+ * rbtree_postorder_for_each_entry_safe() provides a similar guarantee as
+ * list_for_each_entry_safe() and allows the iteration to continue independent
+ * of changes to @pos by the body of the loop.
+ *
+ * Note, however, that it cannot handle other modifications that re-order the
+ * rbtree it is iterating over. This includes calling rb_erase() on @pos, as
+ * rb_erase() may rebalance the tree, causing us to miss some nodes.
*/
+#define rbtree_postorder_for_each_entry_safe(pos, n, root, field) \
+ for (pos = rb_entry_safe(rb_first_postorder(root), typeof(*pos), field); \
+ pos && ({ n = rb_entry_safe(rb_next_postorder(&pos->field), \
+ typeof(*pos), field); 1; }); \
+ pos = n)
+
static inline void rb_erase_init(struct rb_node *n, struct rb_root *root)
{
rb_erase(n, root);
diff --git a/tools/include/linux/rbtree_augmented.h b/tools/include/linux/rbtree_augmented.h
index 43be941db695..d008e1404580 100644
--- a/tools/include/linux/rbtree_augmented.h
+++ b/tools/include/linux/rbtree_augmented.h
@@ -44,7 +44,9 @@ struct rb_augment_callbacks {
void (*rotate)(struct rb_node *old, struct rb_node *new);
};
-extern void __rb_insert_augmented(struct rb_node *node, struct rb_root *root,
+extern void __rb_insert_augmented(struct rb_node *node,
+ struct rb_root *root,
+ bool newleft, struct rb_node **leftmost,
void (*augment_rotate)(struct rb_node *old, struct rb_node *new));
/*
* Fixup the rbtree and update the augmented information when rebalancing.
@@ -60,7 +62,16 @@ static inline void
rb_insert_augmented(struct rb_node *node, struct rb_root *root,
const struct rb_augment_callbacks *augment)
{
- __rb_insert_augmented(node, root, augment->rotate);
+ __rb_insert_augmented(node, root, false, NULL, augment->rotate);
+}
+
+static inline void
+rb_insert_augmented_cached(struct rb_node *node,
+ struct rb_root_cached *root, bool newleft,
+ const struct rb_augment_callbacks *augment)
+{
+ __rb_insert_augmented(node, &root->rb_root,
+ newleft, &root->rb_leftmost, augment->rotate);
}
#define RB_DECLARE_CALLBACKS(rbstatic, rbname, rbstruct, rbfield, \
@@ -93,7 +104,9 @@ rbname ## _rotate(struct rb_node *rb_old, struct rb_node *rb_new) \
old->rbaugmented = rbcompute(old); \
} \
rbstatic const struct rb_augment_callbacks rbname = { \
- rbname ## _propagate, rbname ## _copy, rbname ## _rotate \
+ .propagate = rbname ## _propagate, \
+ .copy = rbname ## _copy, \
+ .rotate = rbname ## _rotate \
};
@@ -126,11 +139,11 @@ __rb_change_child(struct rb_node *old, struct rb_node *new,
{
if (parent) {
if (parent->rb_left == old)
- parent->rb_left = new;
+ WRITE_ONCE(parent->rb_left, new);
else
- parent->rb_right = new;
+ WRITE_ONCE(parent->rb_right, new);
} else
- root->rb_node = new;
+ WRITE_ONCE(root->rb_node, new);
}
extern void __rb_erase_color(struct rb_node *parent, struct rb_root *root,
@@ -138,12 +151,17 @@ extern void __rb_erase_color(struct rb_node *parent, struct rb_root *root,
static __always_inline struct rb_node *
__rb_erase_augmented(struct rb_node *node, struct rb_root *root,
+ struct rb_node **leftmost,
const struct rb_augment_callbacks *augment)
{
- struct rb_node *child = node->rb_right, *tmp = node->rb_left;
+ struct rb_node *child = node->rb_right;
+ struct rb_node *tmp = node->rb_left;
struct rb_node *parent, *rebalance;
unsigned long pc;
+ if (leftmost && node == *leftmost)
+ *leftmost = rb_next(node);
+
if (!tmp) {
/*
* Case 1: node to erase has no more than 1 child (easy!)
@@ -170,6 +188,7 @@ __rb_erase_augmented(struct rb_node *node, struct rb_root *root,
tmp = parent;
} else {
struct rb_node *successor = child, *child2;
+
tmp = child->rb_left;
if (!tmp) {
/*
@@ -183,6 +202,7 @@ __rb_erase_augmented(struct rb_node *node, struct rb_root *root,
*/
parent = successor;
child2 = successor->rb_right;
+
augment->copy(node, successor);
} else {
/*
@@ -204,19 +224,23 @@ __rb_erase_augmented(struct rb_node *node, struct rb_root *root,
successor = tmp;
tmp = tmp->rb_left;
} while (tmp);
- parent->rb_left = child2 = successor->rb_right;
- successor->rb_right = child;
+ child2 = successor->rb_right;
+ WRITE_ONCE(parent->rb_left, child2);
+ WRITE_ONCE(successor->rb_right, child);
rb_set_parent(child, successor);
+
augment->copy(node, successor);
augment->propagate(parent, successor);
}
- successor->rb_left = tmp = node->rb_left;
+ tmp = node->rb_left;
+ WRITE_ONCE(successor->rb_left, tmp);
rb_set_parent(tmp, successor);
pc = node->__rb_parent_color;
tmp = __rb_parent(pc);
__rb_change_child(node, successor, tmp, root);
+
if (child2) {
successor->__rb_parent_color = pc;
rb_set_parent_color(child2, parent, RB_BLACK);
@@ -237,9 +261,21 @@ static __always_inline void
rb_erase_augmented(struct rb_node *node, struct rb_root *root,
const struct rb_augment_callbacks *augment)
{
- struct rb_node *rebalance = __rb_erase_augmented(node, root, augment);
+ struct rb_node *rebalance = __rb_erase_augmented(node, root,
+ NULL, augment);
if (rebalance)
__rb_erase_color(rebalance, root, augment->rotate);
}
-#endif /* _TOOLS_LINUX_RBTREE_AUGMENTED_H */
+static __always_inline void
+rb_erase_augmented_cached(struct rb_node *node, struct rb_root_cached *root,
+ const struct rb_augment_callbacks *augment)
+{
+ struct rb_node *rebalance = __rb_erase_augmented(node, &root->rb_root,
+ &root->rb_leftmost,
+ augment);
+ if (rebalance)
+ __rb_erase_color(rebalance, &root->rb_root, augment->rotate);
+}
+
+#endif /* _TOOLS_LINUX_RBTREE_AUGMENTED_H */
diff --git a/tools/lib/rbtree.c b/tools/lib/rbtree.c
index 17c2b596f043..904adb70a4f0 100644
--- a/tools/lib/rbtree.c
+++ b/tools/lib/rbtree.c
@@ -22,6 +22,7 @@
*/
#include <linux/rbtree_augmented.h>
+#include <linux/export.h>
/*
* red-black trees properties: http://en.wikipedia.org/wiki/Rbtree
@@ -43,6 +44,30 @@
* parentheses and have some accompanying text comment.
*/
+/*
+ * Notes on lockless lookups:
+ *
+ * All stores to the tree structure (rb_left and rb_right) must be done using
+ * WRITE_ONCE(). And we must not inadvertently cause (temporary) loops in the
+ * tree structure as seen in program order.
+ *
+ * These two requirements will allow lockless iteration of the tree -- not
+ * correct iteration mind you, tree rotations are not atomic so a lookup might
+ * miss entire subtrees.
+ *
+ * But they do guarantee that any such traversal will only see valid elements
+ * and that it will indeed complete -- does not get stuck in a loop.
+ *
+ * It also guarantees that if the lookup returns an element it is the 'correct'
+ * one. But not returning an element does _NOT_ mean it's not present.
+ *
+ * NOTE:
+ *
+ * Stores to __rb_parent_color are not important for simple lookups so those
+ * are left undone as of now. Nor did I check for loops involving parent
+ * pointers.
+ */
+
static inline void rb_set_black(struct rb_node *rb)
{
rb->__rb_parent_color |= RB_BLACK;
@@ -70,22 +95,35 @@ __rb_rotate_set_parents(struct rb_node *old, struct rb_node *new,
static __always_inline void
__rb_insert(struct rb_node *node, struct rb_root *root,
+ bool newleft, struct rb_node **leftmost,
void (*augment_rotate)(struct rb_node *old, struct rb_node *new))
{
struct rb_node *parent = rb_red_parent(node), *gparent, *tmp;
+ if (newleft)
+ *leftmost = node;
+
while (true) {
/*
- * Loop invariant: node is red
- *
- * If there is a black parent, we are done.
- * Otherwise, take some corrective action as we don't
- * want a red root or two consecutive red nodes.
+ * Loop invariant: node is red.
*/
- if (!parent) {
+ if (unlikely(!parent)) {
+ /*
+ * The inserted node is root. Either this is the
+ * first node, or we recursed at Case 1 below and
+ * are no longer violating 4).
+ */
rb_set_parent_color(node, NULL, RB_BLACK);
break;
- } else if (rb_is_black(parent))
+ }
+
+ /*
+ * If there is a black parent, we are done.
+ * Otherwise, take some corrective action as,
+ * per 4), we don't want a red root or two
+ * consecutive red nodes.
+ */
+ if(rb_is_black(parent))
break;
gparent = rb_red_parent(parent);
@@ -94,7 +132,7 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
if (parent != tmp) { /* parent == gparent->rb_left */
if (tmp && rb_is_red(tmp)) {
/*
- * Case 1 - color flips
+ * Case 1 - node's uncle is red (color flips).
*
* G g
* / \ / \
@@ -117,7 +155,8 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
tmp = parent->rb_right;
if (node == tmp) {
/*
- * Case 2 - left rotate at parent
+ * Case 2 - node's uncle is black and node is
+ * the parent's right child (left rotate at parent).
*
* G G
* / \ / \
@@ -128,8 +167,9 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
* This still leaves us in violation of 4), the
* continuation into Case 3 will fix that.
*/
- parent->rb_right = tmp = node->rb_left;
- node->rb_left = parent;
+ tmp = node->rb_left;
+ WRITE_ONCE(parent->rb_right, tmp);
+ WRITE_ONCE(node->rb_left, parent);
if (tmp)
rb_set_parent_color(tmp, parent,
RB_BLACK);
@@ -140,7 +180,8 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
}
/*
- * Case 3 - right rotate at gparent
+ * Case 3 - node's uncle is black and node is
+ * the parent's left child (right rotate at gparent).
*
* G P
* / \ / \
@@ -148,8 +189,8 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
* / \
* n U
*/
- gparent->rb_left = tmp; /* == parent->rb_right */
- parent->rb_right = gparent;
+ WRITE_ONCE(gparent->rb_left, tmp); /* == parent->rb_right */
+ WRITE_ONCE(parent->rb_right, gparent);
if (tmp)
rb_set_parent_color(tmp, gparent, RB_BLACK);
__rb_rotate_set_parents(gparent, parent, root, RB_RED);
@@ -170,8 +211,9 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
tmp = parent->rb_left;
if (node == tmp) {
/* Case 2 - right rotate at parent */
- parent->rb_left = tmp = node->rb_right;
- node->rb_right = parent;
+ tmp = node->rb_right;
+ WRITE_ONCE(parent->rb_left, tmp);
+ WRITE_ONCE(node->rb_right, parent);
if (tmp)
rb_set_parent_color(tmp, parent,
RB_BLACK);
@@ -182,8 +224,8 @@ __rb_insert(struct rb_node *node, struct rb_root *root,
}
/* Case 3 - left rotate at gparent */
- gparent->rb_right = tmp; /* == parent->rb_left */
- parent->rb_left = gparent;
+ WRITE_ONCE(gparent->rb_right, tmp); /* == parent->rb_left */
+ WRITE_ONCE(parent->rb_left, gparent);
if (tmp)
rb_set_parent_color(tmp, gparent, RB_BLACK);
__rb_rotate_set_parents(gparent, parent, root, RB_RED);
@@ -223,8 +265,9 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root,
* / \ / \
* Sl Sr N Sl
*/
- parent->rb_right = tmp1 = sibling->rb_left;
- sibling->rb_left = parent;
+ tmp1 = sibling->rb_left;
+ WRITE_ONCE(parent->rb_right, tmp1);
+ WRITE_ONCE(sibling->rb_left, parent);
rb_set_parent_color(tmp1, parent, RB_BLACK);
__rb_rotate_set_parents(parent, sibling, root,
RB_RED);
@@ -268,15 +311,31 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root,
*
* (p) (p)
* / \ / \
- * N S --> N Sl
+ * N S --> N sl
* / \ \
- * sl Sr s
+ * sl Sr S
* \
* Sr
+ *
+ * Note: p might be red, and then both
+ * p and sl are red after rotation(which
+ * breaks property 4). This is fixed in
+ * Case 4 (in __rb_rotate_set_parents()
+ * which set sl the color of p
+ * and set p RB_BLACK)
+ *
+ * (p) (sl)
+ * / \ / \
+ * N sl --> P S
+ * \ / \
+ * S N Sr
+ * \
+ * Sr
*/
- sibling->rb_left = tmp1 = tmp2->rb_right;
- tmp2->rb_right = sibling;
- parent->rb_right = tmp2;
+ tmp1 = tmp2->rb_right;
+ WRITE_ONCE(sibling->rb_left, tmp1);
+ WRITE_ONCE(tmp2->rb_right, sibling);
+ WRITE_ONCE(parent->rb_right, tmp2);
if (tmp1)
rb_set_parent_color(tmp1, sibling,
RB_BLACK);
@@ -296,8 +355,9 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root,
* / \ / \
* (sl) sr N (sl)
*/
- parent->rb_right = tmp2 = sibling->rb_left;
- sibling->rb_left = parent;
+ tmp2 = sibling->rb_left;
+ WRITE_ONCE(parent->rb_right, tmp2);
+ WRITE_ONCE(sibling->rb_left, parent);
rb_set_parent_color(tmp1, sibling, RB_BLACK);
if (tmp2)
rb_set_parent(tmp2, parent);
@@ -309,8 +369,9 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root,
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;
+ tmp1 = sibling->rb_right;
+ WRITE_ONCE(parent->rb_left, tmp1);
+ WRITE_ONCE(sibling->rb_right, parent);
rb_set_parent_color(tmp1, parent, RB_BLACK);
__rb_rotate_set_parents(parent, sibling, root,
RB_RED);
@@ -334,10 +395,11 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root,
}
break;
}
- /* Case 3 - right rotate at sibling */
- sibling->rb_right = tmp1 = tmp2->rb_left;
- tmp2->rb_left = sibling;
- parent->rb_left = tmp2;
+ /* Case 3 - left rotate at sibling */
+ tmp1 = tmp2->rb_left;
+ WRITE_ONCE(sibling->rb_right, tmp1);
+ WRITE_ONCE(tmp2->rb_left, sibling);
+ WRITE_ONCE(parent->rb_left, tmp2);
if (tmp1)
rb_set_parent_color(tmp1, sibling,
RB_BLACK);
@@ -345,9 +407,10 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root,
tmp1 = sibling;
sibling = tmp2;
}
- /* Case 4 - left rotate at parent + color flips */
- parent->rb_left = tmp2 = sibling->rb_right;
- sibling->rb_right = parent;
+ /* Case 4 - right rotate at parent + color flips */
+ tmp2 = sibling->rb_right;
+ WRITE_ONCE(parent->rb_left, tmp2);
+ WRITE_ONCE(sibling->rb_right, parent);
rb_set_parent_color(tmp1, sibling, RB_BLACK);
if (tmp2)
rb_set_parent(tmp2, parent);
@@ -378,22 +441,41 @@ static inline void dummy_copy(struct rb_node *old, struct rb_node *new) {}
static inline void dummy_rotate(struct rb_node *old, struct rb_node *new) {}
static const struct rb_augment_callbacks dummy_callbacks = {
- dummy_propagate, dummy_copy, dummy_rotate
+ .propagate = dummy_propagate,
+ .copy = dummy_copy,
+ .rotate = dummy_rotate
};
void rb_insert_color(struct rb_node *node, struct rb_root *root)
{
- __rb_insert(node, root, dummy_rotate);
+ __rb_insert(node, root, false, NULL, dummy_rotate);
}
void rb_erase(struct rb_node *node, struct rb_root *root)
{
struct rb_node *rebalance;
- rebalance = __rb_erase_augmented(node, root, &dummy_callbacks);
+ rebalance = __rb_erase_augmented(node, root,
+ NULL, &dummy_callbacks);
if (rebalance)
____rb_erase_color(rebalance, root, dummy_rotate);
}
+void rb_insert_color_cached(struct rb_node *node,
+ struct rb_root_cached *root, bool leftmost)
+{
+ __rb_insert(node, &root->rb_root, leftmost,
+ &root->rb_leftmost, dummy_rotate);
+}
+
+void rb_erase_cached(struct rb_node *node, struct rb_root_cached *root)
+{
+ struct rb_node *rebalance;
+ rebalance = __rb_erase_augmented(node, &root->rb_root,
+ &root->rb_leftmost, &dummy_callbacks);
+ if (rebalance)
+ ____rb_erase_color(rebalance, &root->rb_root, dummy_rotate);
+}
+
/*
* Augmented rbtree manipulation functions.
*
@@ -402,9 +484,10 @@ void rb_erase(struct rb_node *node, struct rb_root *root)
*/
void __rb_insert_augmented(struct rb_node *node, struct rb_root *root,
+ bool newleft, struct rb_node **leftmost,
void (*augment_rotate)(struct rb_node *old, struct rb_node *new))
{
- __rb_insert(node, root, augment_rotate);
+ __rb_insert(node, root, newleft, leftmost, augment_rotate);
}
/*
@@ -498,15 +581,24 @@ void rb_replace_node(struct rb_node *victim, struct rb_node *new,
{
struct rb_node *parent = rb_parent(victim);
+ /* Copy the pointers/colour from the victim to the replacement */
+ *new = *victim;
+
/* Set the surrounding nodes to point to the replacement */
- __rb_change_child(victim, new, parent, root);
if (victim->rb_left)
rb_set_parent(victim->rb_left, new);
if (victim->rb_right)
rb_set_parent(victim->rb_right, new);
+ __rb_change_child(victim, new, parent, root);
+}
- /* Copy the pointers/colour from the victim to the replacement */
- *new = *victim;
+void rb_replace_node_cached(struct rb_node *victim, struct rb_node *new,
+ struct rb_root_cached *root)
+{
+ rb_replace_node(victim, new, &root->rb_root);
+
+ if (root->rb_leftmost == victim)
+ root->rb_leftmost = new;
}
static struct rb_node *rb_left_deepest_node(const struct rb_node *node)
--
2.16.4
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