[PATCH] perf symbols: fix slowness due to -ffunction-section

[Eric Saint-Etienne]

Perf can take minutes to parse an image when -ffunction-section is used.
This is especially true with the kernel image when it is compiled this way,
which is the arm64 default since the patcheset "Enable deadcode elimination
at link time".

Perf organize maps using a rbtree. Whenever perf finds a new symbols, it
first searches this rbtree for the map it belongs to, by strcmp()'aring
section names.  When it finds the map with the right name, it uses it to
add the symbol. With a usual image there aren't so many maps but when using
-ffunction-section there's basically one map per function.
With the kernel image that's north of 40,000 maps. For most symbols perf
has to parses the entire rbtree to eventually create a new map and add it.
Consequently perf spends most of the time browsing a rbtree that keeps
getting larger.

This performance fix introduces a secondary rbtree that indexes maps based
on the section name.

Signed-off-by: Eric Saint-Etienne <eric.saint.etienne@xxxxxxxxxx>
Reviewed-by: Dave Kleikamp <dave.kleikamp@xxxxxxxxxx>
Reviewed-by: David Aldridge <david.aldridge@xxxxxxxxxx>
Reviewed-by: Rob Gardner <rob.gardner@xxxxxxxxxx>
---
 tools/perf/util/map.c    | 27 +++++++++++++++++++++++++++
 tools/perf/util/map.h    |  2 ++
 tools/perf/util/symbol.c | 15 +++++++++++++--
 3 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
index 354e545..781eed8 100644
--- a/tools/perf/util/map.c
+++ b/tools/perf/util/map.c
@@ -21,6 +21,7 @@
 #include "unwind.h"
 
 static void __maps__insert(struct maps *maps, struct map *map);
+static void __maps__insert_name(struct maps *maps, struct map *map);
 
 static inline int is_anon_memory(const char *filename, u32 flags)
 {
@@ -496,6 +497,7 @@ u64 map__objdump_2mem(struct map *map, u64 ip)
 static void maps__init(struct maps *maps)
 {
 	maps->entries = RB_ROOT;
+	maps->names = RB_ROOT;
 	init_rwsem(&maps->lock);
 }
 
@@ -664,6 +666,7 @@ size_t map_groups__fprintf(struct map_groups *mg, FILE *fp)
 static void __map_groups__insert(struct map_groups *mg, struct map *map)
 {
 	__maps__insert(&mg->maps, map);
+	__maps__insert_name(&mg->maps, map);
 	map->groups = mg;
 }
 
@@ -824,10 +827,34 @@ static void __maps__insert(struct maps *maps, struct map *map)
 	map__get(map);
 }
 
+static void __maps__insert_name(struct maps *maps, struct map *map)
+{
+	struct rb_node **p = &maps->names.rb_node;
+	struct rb_node *parent = NULL;
+	struct map *m;
+	int rc;
+
+	while (*p != NULL) {
+		parent = *p;
+		m = rb_entry(parent, struct map, rb_node_name);
+		rc = strcmp(m->dso->short_name, map->dso->short_name);
+		if (rc < 0)
+			p = &(*p)->rb_left;
+		else if (rc  > 0)
+			p = &(*p)->rb_right;
+		else
+			return;
+	}
+	rb_link_node(&map->rb_node_name, parent, p);
+	rb_insert_color(&map->rb_node_name, &maps->names);
+	map__get(map);
+}
+
 void maps__insert(struct maps *maps, struct map *map)
 {
 	down_write(&maps->lock);
 	__maps__insert(maps, map);
+	__maps__insert_name(maps, map);
 	up_write(&maps->lock);
 }
 
diff --git a/tools/perf/util/map.h b/tools/perf/util/map.h
index e0f327b..5c792c9 100644
--- a/tools/perf/util/map.h
+++ b/tools/perf/util/map.h
@@ -25,6 +25,7 @@ struct map {
 		struct rb_node	rb_node;
 		struct list_head node;
 	};
+	struct rb_node          rb_node_name;
 	u64			start;
 	u64			end;
 	bool			erange_warned;
@@ -57,6 +58,7 @@ struct kmap {
 
 struct maps {
 	struct rb_root	 entries;
+	struct rb_root	 names;
 	struct rw_semaphore lock;
 };
 
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index d188b75..dcce74b 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -1680,11 +1680,22 @@ struct map *map_groups__find_by_name(struct map_groups *mg, const char *name)
 {
 	struct maps *maps = &mg->maps;
 	struct map *map;
+	struct rb_node *node;
 
 	down_read(&maps->lock);
 
-	for (map = maps__first(maps); map; map = map__next(map)) {
-		if (map->dso && strcmp(map->dso->short_name, name) == 0)
+	for (node = maps->names.rb_node; node; ) {
+		int rc;
+
+		map = rb_entry(node, struct map, rb_node_name);
+
+		rc = strcmp(map->dso->short_name, name);
+		if (rc < 0)
+			node = node->rb_left;
+		else if (rc > 0)
+			node = node->rb_right;
+		else
+
 			goto out_unlock;
 	}
 
-- 
1.8.3.1