perf callchain: Convert children list to rbtree

Current collapse stage has a scalability problem which can be reproduced
easily with a parallel kernel build.

This is because it needs to traverse every children of callchains
linearly during the collapse/merge stage.

Converting it to a rbtree reduced the overhead significantly.

On my 400MB perf.data file which recorded with make -j32 kernel build:

  $ time perf --no-pager report --stdio > /dev/null

before:
  real	6m22.073s
  user	6m18.683s
  sys	0m0.706s

after:
  real	0m20.780s
  user	0m19.962s
  sys	0m0.689s

During the perf report the overhead on append_chain_children went down
from 96.69% to 18.16%:

  -  18.16%  perf  perf                [.] append_chain_children
     - append_chain_children
        - 77.48% append_chain_children
           + 69.79% merge_chain_branch
           - 22.96% append_chain_children
              + 67.44% merge_chain_branch
              + 30.15% append_chain_children
              + 2.41% callchain_append
           + 7.25% callchain_append
        + 12.26% callchain_append
        + 10.22% merge_chain_branch
  +  11.58%  perf  perf                [.] dso__find_symbol
  +   8.02%  perf  perf                [.] sort__comm_cmp
  +   5.48%  perf  libc-2.17.so        [.] malloc_consolidate

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1381468543-25334-2-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 116 insertions, 42 deletions

diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
index 482f68081cd8..e3970e3eaacf 100644
--- a/tools/perf/util/callchain.c
+++ b/tools/perf/util/callchain.c
@@ -21,12 +21,6 @@
 
 __thread struct callchain_cursor callchain_cursor;
 
-#define chain_for_each_child(child, parent)     \
-        list_for_each_entry(child, &parent->children, siblings)
-
-#define chain_for_each_child_safe(child, next, parent)  \
-        list_for_each_entry_safe(child, next, &parent->children, siblings)
-
 static void
 rb_insert_callchain(struct rb_root *root, struct callchain_node *chain,
                     enum chain_mode mode)
@@ -71,10 +65,16 @@ static void
 __sort_chain_flat(struct rb_root *rb_root, struct callchain_node *node,
                   u64 min_hit)
 {
+        struct rb_node *n;
         struct callchain_node *child;
 
-        chain_for_each_child(child, node)
+        n = rb_first(&node->rb_root_in);
+        while (n) {
+                child = rb_entry(n, struct callchain_node, rb_node_in);
+                n = rb_next(n);
+
                 __sort_chain_flat(rb_root, child, min_hit);
+        }
 
         if (node->hit && node->hit >= min_hit)
                 rb_insert_callchain(rb_root, node, CHAIN_FLAT);
@@ -94,11 +94,16 @@ sort_chain_flat(struct rb_root *rb_root, struct callchain_root *root,
 static void __sort_chain_graph_abs(struct callchain_node *node,
                                    u64 min_hit)
 {
+        struct rb_node *n;
         struct callchain_node *child;
 
         node->rb_root = RB_ROOT;
+        n = rb_first(&node->rb_root_in);
+
+        while (n) {
+                child = rb_entry(n, struct callchain_node, rb_node_in);
+                n = rb_next(n);
 
-        chain_for_each_child(child, node) {
                 __sort_chain_graph_abs(child, min_hit);
                 if (callchain_cumul_hits(child) >= min_hit)
                         rb_insert_callchain(&node->rb_root, child,
@@ -117,13 +122,18 @@ sort_chain_graph_abs(struct rb_root *rb_root, struct callchain_root *chain_root,
 static void __sort_chain_graph_rel(struct callchain_node *node,
                                    double min_percent)
 {
+        struct rb_node *n;
         struct callchain_node *child;
         u64 min_hit;
 
         node->rb_root = RB_ROOT;
         min_hit = ceil(node->children_hit * min_percent);
 
-        chain_for_each_child(child, node) {
+        n = rb_first(&node->rb_root_in);
+        while (n) {
+                child = rb_entry(n, struct callchain_node, rb_node_in);
+                n = rb_next(n);
+
                 __sort_chain_graph_rel(child, min_percent);
                 if (callchain_cumul_hits(child) >= min_hit)
                         rb_insert_callchain(&node->rb_root, child,
@@ -173,19 +183,26 @@ create_child(struct callchain_node *parent, bool inherit_children)
                 return NULL;
         }
         new->parent = parent;
-        INIT_LIST_HEAD(&new->children);
         INIT_LIST_HEAD(&new->val);
 
         if (inherit_children) {
-                struct callchain_node *next;
+                struct rb_node *n;
+                struct callchain_node *child;
+
+                new->rb_root_in = parent->rb_root_in;
+                parent->rb_root_in = RB_ROOT;
 
-                list_splice(&parent->children, &new->children);
-                INIT_LIST_HEAD(&parent->children);
+                n = rb_first(&new->rb_root_in);
+                while (n) {
+                        child = rb_entry(n, struct callchain_node, rb_node_in);
+                        child->parent = new;
+                        n = rb_next(n);
+                }
 
-                chain_for_each_child(next, new)
-                        next->parent = new;
+                /* make it the first child */
+                rb_link_node(&new->rb_node_in, NULL, &parent->rb_root_in.rb_node);
+                rb_insert_color(&new->rb_node_in, &parent->rb_root_in);
         }
-        list_add_tail(&new->siblings, &parent->children);
 
         return new;
 }
@@ -223,7 +240,7 @@ fill_node(struct callchain_node *node, struct callchain_cursor *cursor)
         }
 }
 
-static void
+static struct callchain_node *
 add_child(struct callchain_node *parent,
           struct callchain_cursor *cursor,
           u64 period)
@@ -235,6 +252,19 @@ add_child(struct callchain_node *parent,
 
         new->children_hit = 0;
         new->hit = period;
+        return new;
+}
+
+static s64 match_chain(struct callchain_cursor_node *node,
+                      struct callchain_list *cnode)
+{
+        struct symbol *sym = node->sym;
+
+        if (cnode->ms.sym && sym &&
+            callchain_param.key == CCKEY_FUNCTION)
+                return cnode->ms.sym->start - sym->start;
+        else
+                return cnode->ip - node->ip;
 }
 
 /*
@@ -272,9 +302,33 @@ split_add_child(struct callchain_node *parent,
 
         /* create a new child for the new branch if any */
         if (idx_total < cursor->nr) {
+                struct callchain_node *first;
+                struct callchain_list *cnode;
+                struct callchain_cursor_node *node;
+                struct rb_node *p, **pp;
+
                 parent->hit = 0;
-                add_child(parent, cursor, period);
                 parent->children_hit += period;
+
+                node = callchain_cursor_current(cursor);
+                new = add_child(parent, cursor, period);
+
+                /*
+                 * This is second child since we moved parent's children
+                 * to new (first) child above.
+                 */
+                p = parent->rb_root_in.rb_node;
+                first = rb_entry(p, struct callchain_node, rb_node_in);
+                cnode = list_first_entry(&first->val, struct callchain_list,
+                                         list);
+
+                if (match_chain(node, cnode) < 0)
+                        pp = &p->rb_left;
+                else
+                        pp = &p->rb_right;
+
+                rb_link_node(&new->rb_node_in, p, pp);
+                rb_insert_color(&new->rb_node_in, &parent->rb_root_in);
         } else {
                 parent->hit = period;
         }
@@ -291,16 +345,40 @@ append_chain_children(struct callchain_node *root,
                       u64 period)
 {
         struct callchain_node *rnode;
+        struct callchain_cursor_node *node;
+        struct rb_node **p = &root->rb_root_in.rb_node;
+        struct rb_node *parent = NULL;
+
+        node = callchain_cursor_current(cursor);
+        if (!node)
+                return;
 
         /* lookup in childrens */
-        chain_for_each_child(rnode, root) {
-                unsigned int ret = append_chain(rnode, cursor, period);
+        while (*p) {
+                s64 ret;
+                struct callchain_list *cnode;
 
-                if (!ret)
+                parent = *p;
+                rnode = rb_entry(parent, struct callchain_node, rb_node_in);
+                cnode = list_first_entry(&rnode->val, struct callchain_list,
+                                         list);
+
+                /* just check first entry */
+                ret = match_chain(node, cnode);
+                if (ret == 0) {
+                        append_chain(rnode, cursor, period);
                         goto inc_children_hit;
+                }
+
+                if (ret < 0)
+                        p = &parent->rb_left;
+                else
+                        p = &parent->rb_right;
         }
         /* nothing in children, add to the current node */
-        add_child(root, cursor, period);
+        rnode = add_child(root, cursor, period);
+        rb_link_node(&rnode->rb_node_in, parent, p);
+        rb_insert_color(&rnode->rb_node_in, &root->rb_root_in);
 
 inc_children_hit:
         root->children_hit += period;
@@ -325,28 +403,20 @@ append_chain(struct callchain_node *root,
          */
         list_for_each_entry(cnode, &root->val, list) {
                 struct callchain_cursor_node *node;
-                struct symbol *sym;
 
                 node = callchain_cursor_current(cursor);
                 if (!node)
                         break;
 
-                sym = node->sym;
-
-                if (cnode->ms.sym && sym &&
-                    callchain_param.key == CCKEY_FUNCTION) {
-                        if (cnode->ms.sym->start != sym->start)
-                                break;
-                } else if (cnode->ip != node->ip)
+                if (match_chain(node, cnode) != 0)
                         break;
 
-                if (!found)
-                        found = true;
+                found = true;
 
                 callchain_cursor_advance(cursor);
         }
 
-        /* matches not, relay on the parent */
+        /* matches not, relay no the parent */
         if (!found) {
                 cursor->curr = curr_snap;
                 cursor->pos = start;
@@ -395,8 +465,9 @@ merge_chain_branch(struct callchain_cursor *cursor,
                    struct callchain_node *dst, struct callchain_node *src)
 {
         struct callchain_cursor_node **old_last = cursor->last;
-        struct callchain_node *child, *next_child;
+        struct callchain_node *child;
         struct callchain_list *list, *next_list;
+        struct rb_node *n;
         int old_pos = cursor->nr;
         int err = 0;
 
@@ -412,12 +483,16 @@ merge_chain_branch(struct callchain_cursor *cursor,
                 append_chain_children(dst, cursor, src->hit);
         }
 
-        chain_for_each_child_safe(child, next_child, src) {
+        n = rb_first(&src->rb_root_in);
+        while (n) {
+                child = container_of(n, struct callchain_node, rb_node_in);
+                n = rb_next(n);
+                rb_erase(&child->rb_node_in, &src->rb_root_in);
+
                 err = merge_chain_branch(cursor, dst, child);
                 if (err)
                         break;
 
-                list_del(&child->siblings);
                 free(child);
         }
 
diff --git a/tools/perf/util/callchain.h b/tools/perf/util/callchain.h
index 2b585bc308cf..7bb36022377f 100644
--- a/tools/perf/util/callchain.h
+++ b/tools/perf/util/callchain.h
@@ -21,11 +21,11 @@ enum chain_order {
 
 struct callchain_node {
         struct callchain_node   *parent;
-        struct list_head        siblings;
-        struct list_head        children;
         struct list_head        val;
-        struct rb_node          rb_node; /* to sort nodes in an rbtree */
-        struct rb_root          rb_root; /* sorted tree of children */
+        struct rb_node          rb_node_in; /* to insert nodes in an rbtree */
+        struct rb_node          rb_node;    /* to sort nodes in an output tree */
+        struct rb_root          rb_root_in; /* input tree of children */
+        struct rb_root          rb_root;    /* sorted output tree of children */
         unsigned int            val_nr;
         u64                     hit;
         u64                     children_hit;
@@ -86,13 +86,12 @@ extern __thread struct callchain_cursor callchain_cursor;
 
 static inline void callchain_init(struct callchain_root *root)
 {
-        INIT_LIST_HEAD(&root->node.siblings);
-        INIT_LIST_HEAD(&root->node.children);
         INIT_LIST_HEAD(&root->node.val);
 
         root->node.parent = NULL;
         root->node.hit = 0;
         root->node.children_hit = 0;
+        root->node.rb_root_in = RB_ROOT;
         root->max_depth = 0;
 }