[PATCH v2 5/6] perf threads: Switch from rbtree to hashmap

Ian Rogers
2024-02-27T22:02:14Z

The rbtree provides a sorting on entries but this is unused. Switch to
using hashmap for O(1) rather than O(log n) find/insert/remove
complexity.

Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/perf/util/threads.c | 146 ++++++++++++--------------------------
tools/perf/util/threads.h | 6 +-
2 files changed, 47 insertions(+), 105 deletions(-)

diff --git a/tools/perf/util/threads.c b/tools/perf/util/threads.c
index d984ec939c7b..55923be53180 100644
--- a/tools/perf/util/threads.c
+++ b/tools/perf/util/threads.c
@@ -3,25 +3,30 @@
#include "machine.h"
#include "thread.h"

-struct thread_rb_node {
- struct rb_node rb_node;
- struct thread *thread;
-};
-
static struct threads_table_entry *threads__table(struct threads *threads, pid_t tid)
{
/* Cast it to handle tid == -1 */
return &threads->table[(unsigned int)tid % THREADS__TABLE_SIZE];
}

+static size_t key_hash(long key, void *ctx __maybe_unused)
+{
+ /* The table lookup removes low bit entropy, but this is just ignored here. */
+ return key;
+}
+
+static bool key_equal(long key1, long key2, void *ctx __maybe_unused)
+{
+ return key1 == key2;
+}
+
void threads__init(struct threads *threads)
{
for (int i = 0; i < THREADS__TABLE_SIZE; i++) {
struct threads_table_entry *table = &threads->table[i];

- table->entries = RB_ROOT_CACHED;
+ hashmap__init(&table->shard, key_hash, key_equal, NULL);
init_rwsem(&table->lock);
- table->nr = 0;
table->last_match = NULL;
}
}
@@ -32,6 +37,7 @@ void threads__exit(struct threads *threads)
for (int i = 0; i < THREADS__TABLE_SIZE; i++) {
struct threads_table_entry *table = &threads->table[i];

+ hashmap__clear(&table->shard);
exit_rwsem(&table->lock);
}
}
@@ -44,7 +50,7 @@ size_t threads__nr(struct threads *threads)
struct threads_table_entry *table = &threads->table[i];

down_read(&table->lock);
- nr += table->nr;
+ nr += hashmap__size(&table->shard);
up_read(&table->lock);
}
return nr;
@@ -86,28 +92,13 @@ static void threads_table_entry__set_last_match(struct threads_table_entry *tabl
struct thread *threads__find(struct threads *threads, pid_t tid)
{
struct threads_table_entry *table = threads__table(threads, tid);
- struct rb_node **p;
- struct thread *res = NULL;
+ struct thread *res;

down_read(&table->lock);
res = __threads_table_entry__get_last_match(table, tid);
- if (res)
- return res;
-
- p = &table->entries.rb_root.rb_node;
- while (*p != NULL) {
- struct rb_node *parent = *p;
- struct thread *th = rb_entry(parent, struct thread_rb_node, rb_node)->thread;
-
- if (thread__tid(th) == tid) {
- res = thread__get(th);
- break;
- }
-
- if (tid < thread__tid(th))
- p = &(*p)->rb_left;
- else
- p = &(*p)->rb_right;
+ if (!res) {
+ if (hashmap__find(&table->shard, tid, &res))
+ res = thread__get(res);
}
up_read(&table->lock);
if (res)
@@ -118,49 +109,25 @@ struct thread *threads__find(struct threads *threads, pid_t tid)
struct thread *threads__findnew(struct threads *threads, pid_t pid, pid_t tid, bool *created)
{
struct threads_table_entry *table = threads__table(threads, tid);
- struct rb_node **p;
- struct rb_node *parent = NULL;
struct thread *res = NULL;
- struct thread_rb_node *nd;
- bool leftmost = true;

*created = false;
down_write(&table->lock);
- p = &table->entries.rb_root.rb_node;
- while (*p != NULL) {
- struct thread *th;
-
- parent = *p;
- th = rb_entry(parent, struct thread_rb_node, rb_node)->thread;
-
- if (thread__tid(th) == tid) {
- __threads_table_entry__set_last_match(table, th);
- res = thread__get(th);
- goto out_unlock;
- }
-
- if (tid < thread__tid(th))
- p = &(*p)->rb_left;
- else {
- leftmost = false;
- p = &(*p)->rb_right;
- }
- }
- nd = malloc(sizeof(*nd));
- if (nd == NULL)
- goto out_unlock;
res = thread__new(pid, tid);
- if (!res)
- free(nd);
- else {
- *created = true;
- nd->thread = thread__get(res);
- rb_link_node(&nd->rb_node, parent, p);
- rb_insert_color_cached(&nd->rb_node, &table->entries, leftmost);
- ++table->nr;
- __threads_table_entry__set_last_match(table, res);
+ if (res) {
+ if (hashmap__add(&table->shard, tid, res)) {
+ /* Add failed. Assume a race so find other entry. */
+ thread__put(res);
+ res = NULL;
+ if (hashmap__find(&table->shard, tid, &res))
+ res = thread__get(res);
+ } else {
+ res = thread__get(res);
+ *created = true;
+ }
+ if (res)
+ __threads_table_entry__set_last_match(table, res);
}
-out_unlock:
up_write(&table->lock);
return res;
}
@@ -169,57 +136,32 @@ void threads__remove_all_threads(struct threads *threads)
{
for (int i = 0; i < THREADS__TABLE_SIZE; i++) {
struct threads_table_entry *table = &threads->table[i];
- struct rb_node *nd;
+ struct hashmap_entry *cur, *tmp;
+ size_t bkt;

down_write(&table->lock);
__threads_table_entry__set_last_match(table, NULL);
- nd = rb_first_cached(&table->entries);
- while (nd) {
- struct thread_rb_node *trb = rb_entry(nd, struct thread_rb_node, rb_node);
-
- nd = rb_next(nd);
- thread__put(trb->thread);
- rb_erase_cached(&trb->rb_node, &table->entries);
- RB_CLEAR_NODE(&trb->rb_node);
- --table->nr;
+ hashmap__for_each_entry_safe((&table->shard), cur, tmp, bkt) {
+ struct thread *old_value;

- free(trb);
+ hashmap__delete(&table->shard, cur->key, /*old_key=*/NULL, &old_value);
+ thread__put(old_value);
}
- assert(table->nr == 0);
up_write(&table->lock);
}
}

void threads__remove(struct threads *threads, struct thread *thread)
{
- struct rb_node **p;
struct threads_table_entry *table = threads__table(threads, thread__tid(thread));
- pid_t tid = thread__tid(thread);
+ struct thread *old_value;

down_write(&table->lock);
if (table->last_match && RC_CHK_EQUAL(table->last_match, thread))
__threads_table_entry__set_last_match(table, NULL);

- p = &table->entries.rb_root.rb_node;
- while (*p != NULL) {
- struct rb_node *parent = *p;
- struct thread_rb_node *nd = rb_entry(parent, struct thread_rb_node, rb_node);
- struct thread *th = nd->thread;
-
- if (RC_CHK_EQUAL(th, thread)) {
- thread__put(nd->thread);
- rb_erase_cached(&nd->rb_node, &table->entries);
- RB_CLEAR_NODE(&nd->rb_node);
- --table->nr;
- free(nd);
- break;
- }
-
- if (tid < thread__tid(th))
- p = &(*p)->rb_left;
- else
- p = &(*p)->rb_right;
- }
+ hashmap__delete(&table->shard, thread__tid(thread), /*old_key=*/NULL, &old_value);
+ thread__put(old_value);
up_write(&table->lock);
}

@@ -229,11 +171,11 @@ int threads__for_each_thread(struct threads *threads,
{
for (int i = 0; i < THREADS__TABLE_SIZE; i++) {
struct threads_table_entry *table = &threads->table[i];
- struct rb_node *nd;
+ struct hashmap_entry *cur;
+ size_t bkt;

- for (nd = rb_first_cached(&table->entries); nd; nd = rb_next(nd)) {
- struct thread_rb_node *trb = rb_entry(nd, struct thread_rb_node, rb_node);
- int rc = fn(trb->thread, data);
+ hashmap__for_each_entry((&table->shard), cur, bkt) {
+ int rc = fn((struct thread *)cur->pvalue, data);

if (rc != 0)
return rc;
diff --git a/tools/perf/util/threads.h b/tools/perf/util/threads.h
index ed67de627578..d03bd91a7769 100644
--- a/tools/perf/util/threads.h
+++ b/tools/perf/util/threads.h
@@ -2,7 +2,7 @@
#ifndef __PERF_THREADS_H
#define __PERF_THREADS_H

-#include <linux/rbtree.h>
+#include "hashmap.h"
#include "rwsem.h"

struct thread;
@@ -11,9 +11,9 @@ struct thread;
#define THREADS__TABLE_SIZE (1 << THREADS__TABLE_BITS)

struct threads_table_entry {
- struct rb_root_cached entries;
+ /* Key is tid, value is struct thread. */
+ struct hashmap shard;
struct rw_semaphore lock;
- unsigned int nr;
struct thread *last_match;
};

--
2.44.0.rc1.240.g4c46232300-goog